Color Measurement and Matching of Plastics (CIELAB, Delta E, Metamerism): 5 Delta E Formulas and 7 Additive Groups That Shift Color

Color in plastics is measured as CIELAB L*, a* and b* coordinates and compared to a standard as a Delta E color difference, calculated under ASTM D2244-25 with one of 5 formulas, and 7 groups of additives move the result. Colorants make up only 0.01 to 5 wt% of a plastic product (Chea et al., 2025), so why can two laboratories measure the same plaque against the same master and disagree about whether it passes? The formula, illuminant, observer and geometry decide the number, and metamerism decides whether a daylight match holds under store light.

White pigments such as titanium dioxide and black pigments such as carbon black set lightness, color pigments and dyes set hue and chroma, optical brighteners add fluorescence, antioxidants and stabilizers shift yellowness and pinkness, effect pigments change color with angle, and functional additives such as laser-marking, reheat and oxygen-scavenger additives shift color as a side effect.

This guide to color measurement of plastics, or colour measurement in British usage, covers Delta E and CIELAB, the 5 formulas, measuring conditions, metamerism, matching and tolerancing, how 7 groups of plastic additives move each coordinate, the values per application and the limits of the number.

The 12 properties that define a color reading on a plastic are summarized in Table 1.

Standard editions are the versions current on 24 October 2026. No pass/fail Delta E is given because every standard listed here leaves the tolerance to the color specification.

What Is Delta E Color Difference?#

Delta E (ΔE) is the size of the color difference between a sample and its standard, expressed as one number calculated from instrumentally measured color coordinates, and ASTM D2244-25 is the practice that defines the calculation for opaque specimens such as plastic plaques. ASTM D2244-25 has been the active edition since 10 June 2025, superseding D2244-23, and its equations are based on daylight illumination.

If Delta E reduces a color difference to one number, how does a colorist know which way to correct the recipe? ASTM D2244-25 notes that the scalar decides whether a specimen is within tolerance, while the three components, the lightness, chroma and hue differences, give the direction of the departure.

CIELAB: the L*, a* and b* coordinates behind every Delta E#

CIELAB is the color space the CIE defined in 1976 so that equal distances look more nearly like equal color differences, and it describes every color with three coordinates: lightness L*, the red-green coordinate a* and the yellow-blue coordinate b*. ISO/CIE 11664-4:2019 now specifies its coordinates, which are calculated from the tristimulus values X, Y and Z. The three CIELAB axes are listed below.

• L*: lightness, from 0 for black to 100 for white; carbon black and titanium dioxide move it most.
• a*: the red-green coordinate, positive toward red and negative toward green; a white compound that pinks moves toward positive a*.
• b*: the yellow-blue coordinate, positive toward yellow and negative toward blue; a yellowing compound moves toward positive b*, an optical brightener or a blue toner toward negative b*.

The same space is often reported as L*C*h, with chroma C* = √(a*² + b*²) and hue angle h = atan(b*/a*), the terms a colorist corrects in. CIELAB lacks perceptual uniformity, particularly in the blue hues, and ASTM E308-22 states that the CIE systems "are not intended to provide visually uniform scales", which is why the weighted formulas below exist.

Are Delta E and Delta H the same thing?#

No: Delta E is the total color difference, while Delta H (ΔH*) is only its hue component, one of the three parts, with the lightness difference ΔL* and the chroma difference ΔC*, that make up the total. A compound can show a small Delta E and still be rejected for hue, because ΔH* shows whether the shade has drifted toward a neighboring hue.

How to calculate Delta E: the CIE76 formula#

The basic Delta E is calculated as the straight-line distance between the standard and the sample in CIELAB, ΔE*ab = √[(ΔL*)² + (Δa*)² + (Δb*)²], where ΔL*, Δa* and Δb* are the sample's coordinates minus the standard's. ASTM E308-22 converts the measured spectral data into CIELAB beforehand. The 3 steps of the calculation are listed below.

1. Measure the standard and the sample on the same instrument, with the same illuminant, observer and geometry.
2. Subtract the standard's L*, a* and b* from the sample's to get ΔL*, Δa* and Δb*.
3. Square the three differences, add them and take the square root.

One ΔE*ab limit is stricter on one color than on the next, because CIELAB is not perfectly uniform, so ASTM D2244-25 adds four weighted formulas.

What Delta E value can the eye see?#

A difference of about 2.3 ΔE*ab is often quoted as the just-noticeable difference, a figure given by Gaurav Sharma in the Digital Color Imaging Handbook (2003), but no standard turns that figure into a pass mark for a plastic part. ASTM D2244-25 leaves the tolerance to the purchaser and the seller, and published perception scales differ between sources and formulas.

The 5 Delta E Formulas in ASTM D2244#

The 5 Delta E formulas in ASTM D2244-25 are CIELAB ΔE*ab, CMC l:c, CIE94, DIN99o and CIEDE2000, and the standard highly recommends CIEDE2000 (ΔE00) for the small differences of 0.0 to 5.0 ΔE*ab that decide most plastic color approvals. Each weighted formula brings the number closer to visual judgment, and each gives a different value for the same pair of plaques.

Table 2 compares the 5 formulas in the order ASTM D2244-25 lists them.

ASTM D2244-25 names all 5 formulas. Their values for the same pair of specimens differ, and the standard states that there is no simple factor that converts one into another.

1. CIELAB ΔE*ab (CIE 1976)#

CIELAB ΔE*ab is the unweighted distance between two colors in L*a*b* space, and its weakness is that the same number does not look the same size everywhere in color space. Plastics data sheets still print it because it needs no parameters, so any software reproduces the same value. A ΔE*ab of the same size can nevertheless be acceptable on a saturated red and visible on a near-neutral grey.

2. CMC l:c#

CMC l:c is the tolerance formula the Colour Measurement Committee of the Society of Dyers and Colourists defined in 1984, and it draws an ellipsoid around the standard instead of a sphere, so that a difference in hue counts for more than the same difference in lightness. A ratio l:c of 2:1 is commonly used for acceptability decisions and 1:1 for the threshold of perceptibility. The pair is stated with the result, as ΔEcmc(2:1), or two laboratories are not computing the same number. ASTM D2244-25 reports that its tolerance equations were tested against visual data for textiles and plastics.

3. CIE94#

CIE94 is the CIE's 1994 formula that weights the lightness, chroma and hue differences separately, with a lightness factor kL of 1 for graphic arts and 2 for textiles. A new plastics specification rarely chooses it, because ASTM D2244-25 recommends ΔE00 for the small-difference range and CIEDE2000 extends the same weighting idea with further corrections.

4. DIN99o#

DIN99o is the color difference formula of the German standard DIN 6176, and it is the fourth of the formulas ASTM D2244-25 accepts. It calculates the difference in a transformed version of the CIELAB space, so a specification that uses DIN99o names it explicitly, because no other formula converts into it.

5. CIEDE2000 (ΔE00)#

CIEDE2000 (ΔE00) is the formula ASTM D2244-25 highly recommends for color differences between 0.0 and 5.0 ΔE*ab, because it corrects CIELAB where the eye disagrees with it most: in the blues, in near-neutral greys and in the balance between lightness, chroma and hue.

CIEDE2000 is published as ISO/CIE 11664-6:2022, the second edition replacing 2014, based on CIE 142-2001. ASTM D2244-25 names plastics among the industries where ΔE00 is appropriate and widely used, alongside automobiles, coatings, packaging and textiles. A new color specification should state ΔE00 unless an existing customer standard already fixes another formula.

Can Delta E values from different formulas be compared?#

No: ASTM D2244-25 states that color differences for the same specimens are not likely to be identical in two different formulas and that there is no simple factor to convert one into another, so a ΔE00 of 1.0 and a ΔE*ab of 1.0 are not the same tolerance. A supplier's certificate and the customer's specification therefore name the same formula, and for CMC the same l:c ratio, or the comparison is meaningless.

How Is Color Measured on a Plastic? Instrument, Illuminant, Observer and Geometry#

Color is measured on a plastic with a spectrophotometer or a colorimeter, under a stated CIE illuminant, for a stated CIE observer, in a stated measuring geometry, and those 4 settings decide whether two L*a*b* readings of the same part can be compared at all. ASTM E805-22 is the practice for documenting these settings, and ASTM E179-17(2022) warns that geometric variables "can importantly affect instrumentally measured values of color". Color measurement belongs to the optical, color and dispersion group of the methods for testing plastic additives. Every Delta E on a certificate should carry the instrument type, the geometry with its specular mode, the illuminant and observer, and the formula.

Table 3 lists the 6 settings behind a color reading, with the reference that governs each one.

"d/8", "SCI" and "SCE" are common instrument labels for sphere geometry with the specular component included or excluded; the standards cited describe the geometry, not the labels.

Spectrophotometer or colorimeter#

A spectrophotometer records the full reflectance curve of the plastic across the visible spectrum and a tristimulus colorimeter records only three filtered signals, so only the spectrophotometer can show that two matching parts are metameric. ASTM E1164-23 covers how that spectral data is obtained, and ASTM E308-22 converts it into CIELAB for any CIE illuminant without remeasuring the part.

ASTM E1347-06(2020) states that tristimulus colorimeters "cannot be used to gain any information about metamerism or paramerism" and restricts them to specimens of similar spectral and geometric characteristics, standardized against a product standard. A colorimeter therefore checks a running production color against its own master, and a spectrophotometer matches a new color or approves a pigment change.

Illuminant and observer: D65, 10° and the other CIE conditions#

D65 with the 10° observer is the usual starting point for plastics, because ISO/CIE 11664-2:2022 makes D65 the illuminant for representative daylight and ASTM D2244-25 derives its color difference equations for daylight. ISO/CIE 11664-2:2022 defines these illuminants with spectral data from 300 to 830 nm. ISO/CIE 11664-1:2019 defines the CIE 1931 observer for fields of about 1° to 4° and the CIE 1964 observer for fields above about 4°; a molded part held at arm's length fills more than 4°, hence "D65/10°". The 4 illuminant types a plastic part typically meets are listed below.

• D65: average daylight at about 6,500 K, the basis of the D2244-25 equations.
• Illuminant A: tungsten-filament light at about 2,856 K, the classic second illuminant for a metamerism check.
• F11: a narrow tri-band fluorescent lamp at 4,000 K, equated in secondary sources with the TL84 store lamp.
• LED illuminants: nine series in CIE 015:2018 (Colorimetry, 4th edition), from about 2,700 to 6,600 K.

Measuring geometry: integrating sphere or 45:0, specular included or excluded#

A sphere instrument is the choice for colorant formulation and a 45:0 instrument for judging appearance, because a sphere can include the gloss reflection in the reading while a 45:0 instrument sees the part roughly as an eye does under a single directional light. ASTM E1331-15(2023) suits the sphere to computer colorant formulation, recommends excluding the specular component for color assessment of plane high-gloss specimens, and advises against it for intermediate gloss. A matte and a glossy molding of one compound therefore read differently with the specular component excluded, so texture and gloss belong on the color specification.

ASTM E1349-06(2022) covers 45:0 and 0:45 geometry for flat, non-fluorescent specimens of any gloss, is recommended for intermediate gloss and is not for bare metal surfaces.

Specimens: plaques, pellets, film and transparent parts#

The specimen form changes the reading as much as the instrument does, so a standard and a sample are compared only in the same form, at the same thickness and with the same surface texture. ASTM E313-20 (reapproved 2025) applies the same rule to its own index: same material and general appearance, similar gloss and texture, and equal thickness when not opaque. The 4 specimen forms used for plastics are listed below.

• Molded plaques: the opaque specimen ASTM D2244-25 names, and the usual form of a color master.
• Pellets: measured under ASTM D6290-19 for yellowness and L*a*b* of natural and near-white, non-fluorescent resins at incoming inspection.
• Film and sheet: compared at equal thickness, because thickness changes how much light passes through a part that is not fully opaque.
• Transparent parts: measured in transmitted light, which ASTM E1347-06(2020) provides for; their haze is a separate test.

What Is Metamerism, and How Is It Checked on Plastics?#

Color metamerism is the effect in which two plastic parts match under one light source and mismatch under another, and it happens because the two parts reach the same color with different reflectance curves, usually because they contain different pigments. Ampacet, a masterbatch producer, gives two plastics examples across the visible spectrum of 400 to 700 nm: bottles or extruded film matched under sodium-arc lamps that mismatch in daylight, and a repainted car fender that matches in daylight and fails under mercury-vapor lamps.

If a spectrophotometer reports a ΔE00 inside tolerance under D65, how can the part still fail at the customer's store? ASTM D2244-25 derives its equations for daylight and calls for visual confirmation of metamerism under ASTM D4086 whenever other illuminants matter.

Illuminant, observer and geometric metamerism#

Metamerism appears in 4 forms that matter on plastics: illuminant metamerism, observer metamerism, geometric metamerism and the device differences between two instruments. The four forms are listed below.

• Illuminant metamerism: the pair matches under one light source and fails under another; the form ASTM D4086-18(2023) checks.
• Observer metamerism: the pair matches for one observer and not for another with different color vision, including the change between small and large viewing fields; the second form D4086 covers.
• Geometric metamerism: the pair matches at one viewing angle and fails at another, typical of metallic and pearlescent parts and outside the scope of D4086.
• Instrument (device) differences: two instruments disagree on the same pair, a form named in secondary colorimetry sources; a tristimulus colorimeter cannot settle a metamerism question at all.

The visual check: ASTM D4086 and ASTM D1729#

Metamerism is checked visually: ASTM D4086-18(2023) gives the methods for detecting it and estimating its size, and ASTM D1729-22 sets the equipment, the diffuse illumination and the observer requirements for judging the pair. ASTM D4086-18(2023), active since 28 November 2023, covers illuminant and observer metamerism only and excludes gonioapparent samples. The 3 steps of a visual metamerism check are listed below.

1. View the standard and the sample side by side under diffuse daylight-type illumination, with an observer of tested color vision.
2. Switch to a second light source with a different spectrum and look again.
3. Record a pair that changes between the two sources as metameric, and estimate the size of the change.

ASTM D1729-22 asks for observers with at least normal color vision, preferably superior on the FM-100 Hue Test (Guide E1499), and excludes metallic and pearlescent materials.

Why replacing a lead chromate or cadmium pigment causes metamerism#

Replacing a lead chromate or cadmium pigment causes metamerism because the heavy-metal-free pigments that reach the same yellow, orange or red under daylight do it with a different reflectance curve, so the new compound can match under D65 and drift under store or tungsten light. Ampacet names metamerism as the issue to address in every switch from heavy-metal-containing to heavy-metal-free color masterbatch.

Lead chromate (CAS 7758-97-6), PY34 and PR104 have been on the REACH SVHC Candidate List since 13 January 2010 and in Annex XIV of Regulation (EC) No 1907/2006 (entries 10 to 12) with a sunset date of 21 May 2015, so EU use needs an authorisation; the history of lead chromate is on its substance page. Cadmium sulphide has been an SVHC since 16 December 2013, REACH Annex XVII entry 23 limits cadmium in listed plastics to 0.01 % by weight, and Regulation (EU) 2025/40 (PPWR) Art. 5(4) caps lead, cadmium, mercury and hexavalent chromium in packaging at 100 mg/kg combined from 12 August 2026. Bismuth vanadate (PY184) is one lead-free replacement yellow, and Ampacet advises matching with pigments of the closest possible reflectance.

Is a metameric match always rejected?#

No: a metameric match can be accepted when it holds under the lighting the product is actually displayed and used in, which is why Ampacet advises the supplier and the customer to agree those light sources before the match is made. The illuminants on the color specification should therefore include the store or use lighting, not only D65.

How Is a Color Match Made for a Plastic?#

A color match for a plastic is made in 6 steps, from measuring the customer's standard to approving a production trial, and the same base resin, let-down ratio and processing conditions have to be used at every step. The 6 steps are listed below.

1. Measure the customer's standard with a spectrophotometer under the agreed illuminants, observer and geometry.
2. Select pigments and dyes that survive the processing temperature, meet the regulatory route and follow the standard's reflectance curve.
3. Formulate a first recipe, often by computer colorant formulation from the spectral data.
4. Let down the recipe into the customer's base resin and mold a plaque at production thickness.
5. Compare the plaque to the standard in the agreed Delta E formula and visually under at least two light sources.
6. Approve, then hold production lots to the agreed tolerance against the same master.

Ampacet notes that FDA compliance, outdoor exposure performance and high thermal stability each narrow the usable pigment palette and can raise the cost of a color formulation. Most matches reach the part as a color masterbatch, whose carrier and let-down are covered under color masterbatch.

Setting the color tolerance: an agreed limit, not a universal number#

A color tolerance for a plastic is a limit the purchaser and the seller agree, together with the formula used to calculate it, because ASTM D2244-25 sets no universal value and notes that gloss, texture and how close the parts sit to each other change what difference is acceptable. Each material and condition of use can need its own tolerance.

ASTM D2244-25 asks that instrumental tolerances be correlated with visual appraisal under ASTM D1729-22, and reports that its equations misclassify a difference no more often than the most experienced visual color matcher. A specification can also set separate limits on ΔL*, ΔC* and ΔH*, because the scalar alone hides the direction. A new tolerance should be confirmed visually under ASTM D1729-22 before it is written into a specification.

Let-down ratio, dispersion and tinting strength: why a matched color drifts#

A matched color drifts in production for 3 reasons: the masterbatch is dosed at a different let-down ratio than in the lab, the pigment is dispersed less completely, or the pigment lot has a different tinting strength.

A color masterbatch is usually added at 1 to 5 %, and the two conventions differ: 5 % as a percentage equals 19:1 as a ratio, according to Ampacet. A dosing error therefore moves lightness and chroma directly, and the let-down ratio converts between the two conventions with the let-down ratio calculator. Liquid color dosed by peristaltic pump is chosen where accurate dosing and quick color changes matter.

Dispersion and pigment strength cause the other two drifts. An undispersed agglomerate adds no color, so the same loading gives a weaker shade. A pigment lot with a different tinting strength shifts the shade at the same dosage.

How Do Additives Shift the Color of a Plastic? 7 Additive Groups#

Additives shift the color of a plastic in 7 groups: white pigments, black pigments, color pigments and dyes, optical brighteners, antioxidants and stabilizers, effect pigments and functional additives with a color side effect, and only the first three are added to set the color on purpose. The chemistry of each class of colorants is on colorants for plastics, while Table 4 shows what each group does to a color reading.

Directions and examples are from the cited sources at the stated loading. No source in our set gives a Delta E per wt% of any pigment or stabilizer, so none is printed.

1. White pigments: titanium dioxide and white masterbatch#

Titanium dioxide raises the lightness L* and the opacity of a plastic because its high refractive index scatters visible light strongly, with the strongest scattering at a crystal size of about 220 nm. It is supplied as rutile and anatase (Pigment White 6, CAS 13463-67-7), and the grades and surface treatments of titanium dioxide decide both its opacity and its pinking risk.

Pinking is the color fault it can cause. Low-treated rutile grades can catalyse the over-oxidation of phenolic antioxidants to colored complexes, read as a rise in a*, and Ampacet lists zinc stearate as the additive that forms colorless complexes instead. Ampacet also reports that few low-treated rutile grades suit extrusion above 274 °C (525 °F).

Most titanium dioxide reaches the part predispersed as white masterbatch.

2. Black pigments: carbon black, L* and NIR sorting#

Carbon black lowers the lightness L* of a plastic because it absorbs across the whole visible spectrum, and the finer its primary particles, the deeper the black and the harder it is to disperse. It also absorbs ultraviolet, and PE pressure pipe carries 2.0 to 2.5 wt%; grades of carbon black in plastics are compared by particle size and jetness.

L* is now a recyclability number. The APR Design Guide test SORT-S-01 fails dark colors with L* below 40 or a near-infrared reflectance of 10 % or less, because carbon black absorbs the signal NIR sorters rely on. The fix for a failing L* is one of the NIR-sortable black colorants.

3. Color pigments and dyes: organic, inorganic and solvent-dye shades#

Color pigments and dyes set the hue and chroma of a plastic in two different ways: pigments such as phthalocyanine blue, quinacridone and bismuth vanadate stay as dispersed particles that absorb and scatter, while solvent dyes dissolve and give transparent shades with no scattering. The azo and polycyclic pigment classes are compared under organic pigments for plastics, and Lanxess lists its Macrolex solvent dyes for amorphous polymers such as PS, ABS, PMMA, PC and PET.

A pigment pushed past its heat stability changes shade during processing. Diarylide yellows such as PY83 degrade above about 200 °C (392 °F), can release 3,3'-dichlorobenzidine, and their decomposition products are implicated in the yellowing of recycled PE.

4. Optical brighteners: fluorescence and the UV in the light source#

Optical brighteners lower the yellowness b* of a plastic by absorbing ultraviolet light at about 340 to 370 nm and re-emitting it as blue light at about 420 to 470 nm, so their effect on a color reading depends on how much UV the instrument's light source contains. Mayzo gives 50 to 1,000 ppm of OB-1 (CAS 1533-45-5) for polyester, polyamide and polycarbonate; grades and food-contact limits are on optical brighteners for plastics.

ASTM E1331-15(2023) advises against sphere measurement of fluorescent specimens when the highest accuracy is needed, ASTM E1349-06(2022) and ASTM D6290-19 cover non-fluorescent specimens only, and fluorescent object color has its own practices, ASTM E991 and ASTM E2153. A blue toner such as ultramarine blue neutralizes yellowness by absorption instead, so it reads the same under any light source.

5. Antioxidants and stabilizers: yellowing, pinking and gas fading#

Antioxidants and stabilizers shift color in 3 ways that a spectrophotometer reads directly: yellowing as a rise in b*, pinking as a rise in a*, and gas fading, the yellow or pink discoloration that nitrogen oxides from gas-fired equipment cause in phenolic antioxidants. Phenolic antioxidants such as BHT over-oxidize to colored quinones or, with nitrogen oxides, to quinone methides; low-discoloration grades are compared under phenolic antioxidants.

Phosphites such as Irgafos 168 prevent thermally induced discoloration and are usable in gas-fired ovens, according to BASF, phenol-free hydroxylamine and phosphite systems prevent gas fading, and aminic antioxidants are avoided where color matters because they discolor strongly. In PVC, 0.1 % dehydrochlorination already gives unacceptable discoloration. The full diagnosis is under why plastics turn yellow or pink.

6. Effect pigments: metallic and pearlescent color that changes with angle#

Effect pigments such as aluminium flake and coated mica make the color of a plastic depend on the viewing angle, so a single-angle instrument cannot describe them and ASTM E2194-14(2025) uses three measuring angles for metal-flake materials. Aluminium flake reflects specularly, and mica coated with titanium dioxide or iron oxide gives pearlescent interference; flake types are on effect pigments (pearlescent, metallic).

ASTM E2539-25 covers interference pigments, and ASTM E2194-14(2025) warns that equal values at three angles do not guarantee a visual match when gloss, texture or flake orientation differ. Neither ASTM D1729-22 nor ASTM D4086-18(2023) covers these materials.

7. Functional additives with a color side effect: laser marking, reheat and oxygen scavengers#

Functional additives bought for another purpose shift color in 3 documented cases: laser-marking additives create a deliberate local color difference, reheat additives can darken or yellow PET, and oxygen scavengers can raise the b* of a clear bottle. In laser marking, ΔE is the performance number: Lu and co-workers (ACS Omega, 2020) raised the marking contrast in ABS from ΔE 7 to 25 at a 7 A laser current with 1 to 8 wt% organo-montmorillonite, explained further under laser marking additives.

The APR places reheat additives in its "Requires Testing" category for PET because they "can turn flake dark or yellow", and their dose rates are on IR absorbers and reheat additives.

Avient states that its Amosorb 4020G oxygen scavenger halves the b* shift of previous grades, a supplier claim. Nigrosine, used in black polyamides, can also discolor PA66 and slow its crystallization (Polymers, 2025).

Which Color Values Matter for Each Plastic and Application?#

The color value that matters depends on the application: L* decides whether dark packaging can be sorted, b* decides whether a clear PET bottle or a natural resin looks yellow, a full Delta E against a master decides a molded part, and ΔL decides how visible a scratch is. Table 6 lists the value each application is judged on.

The table names the value each application is judged on. Pass limits come from the customer specification and are not given here.

Packaging turns color into a recycling number: L* below 40 fails APR NIR sorting and reheat additives can darken PET flake, so recyclate color is read alongside the stabilizer packages on additives for recycled plastics.

Automotive and appliance parts are approved on a Delta E against a master, and metallic trim needs multi-angle measurement; ASTM D2244-25 names automobiles among the industries using ΔE00. Interior and exterior packages are on additives for automotive plastics.

Scratch visibility on textured automotive plastics is read as a lightness difference ΔL, with the procedure taken from the customer's specification. The stylus procedures behind a ΔL rating are on scratch resistance testing of plastics.

What Delta E Cannot Tell You#

A Delta E cannot answer 5 questions that color specifications regularly put to it, and each one needs a second light source, a second angle or a second test. The 5 questions are listed below with what answers each.

• Whether the match holds under another light: the D2244-25 equations are derived for daylight, so a visual check to ASTM D4086-18(2023) is needed.
• Whether a difference is acceptable: gloss, texture and proximity change acceptability, so the tolerance comes from visual appraisal under ASTM D1729-22.
• Whether a metallic or pearlescent part matches: one geometry cannot describe an angle-dependent color, so multi-angle measurement is needed.
• How yellow a near-white part looks: that is the yellowness index of ASTM E313-20 (reapproved 2025), a single-number scale.
• Whether the color lasts: a ΔE after exposure records a change that has already happened, produced by the exposure tests in the next section.

For near-white parts, the number buyers use is the yellowness index, a single-number test rather than a difference from a master.

Which Other Tests Are Run Alongside Color Measurement?#

A color reading is read next to 4 other tests, because Delta E says how far a part is from its master while the other four say how yellow, how durable, how clear or glossy, and how well dispersed it is. The map of testing plastic additives and additive-dependent properties shows which of the 42 test methods answers which question.

Yellowness and whiteness index#

The yellowness index condenses the color of a near-white or clear plastic into one number under ASTM E313-20 (reapproved 2025), valid for specimens with a dominant wavelength of 570 to 580 nm, and the whiteness index covers whites with a CIE Y above 65. ASTM D1925 was withdrawn in 1995 and is never cited as current, and for pellets ASTM D6290-19 and ISO 17223 address the same subject but differ in technical content. Formula pitfalls are covered under yellowness index testing.

Accelerated weathering and pigment fastness#

Accelerated weathering produces the color change that a Delta E then measures: the specimen is exposed in a xenon-arc or fluorescent UV device under ISO 4892-2, ASTM G155-25, ASTM G154-23, ASTM D2565 or ASTM D4329-26, and the color shift is reported with the other endpoints. Cycles and irradiance are on accelerated weathering tests. Heat stability, lightfastness and weather resistance of each pigment are rated on pigment fastness in plastics.

Haze, gloss and opacity#

Haze, gloss and opacity are measured separately from color because they describe how light is scattered rather than which wavelengths are absorbed: haze under ASTM D1003-21, gloss under ASTM D523 or ISO 2813. ASTM D1003-21 uses a hazemeter (procedure A) or a spectrophotometer (procedure B), compared on haze and clarity measurement.

Gloss also feeds back into a color reading through the specular component, and it is set deliberately with matting agents and gloss modifiers. The term opacity is defined in the glossary; no plastics opacity standard is verified in our sources.

Dispersion testing of pigments and masterbatch#

Dispersion testing explains a weak or speckled color before the spectrophotometer does: a filter pressure value in bar per gram of pigment and a microdispersion rating on thin film both show agglomerates that add no color. The filter pressure value follows the EN 13900 series, and Ampacet rates black masterbatch on a scale of 1 to 5 (1 best) on about 1.5 mil (38 µm) film. Both methods are compared on dispersion testing of pigments and masterbatch, and pigment wetting in a masterbatch improves with dispersing agents for plastics and masterbatch.

Color questions from buyers and designers#

Three questions about plastic color come from outside the laboratory, and each has a short answer.

How can you add color to plastic?#

Color is added to plastic during processing, as a color masterbatch let down at about 1 to 5 %, as liquid color dosed by pump, or as a compound that is already colored, and uncolored resin is sold as natural. Producers are listed under color masterbatch manufacturers.

What are the color codes for plastic?#

A plastic color is specified by a physical master with its measured L*a*b* values and an agreed tolerance, while the pigments inside it are identified by Colour Index names such as Pigment Blue 15:3. How such a name is built is explained under Colour Index (C.I.) pigment names.

Is Delta E for monitors and printing the same number as for plastics?#

The calculation is the same family of CIE formulas, but a monitor's Delta E compares emitted colors on a screen, while a plastic's Delta E compares light reflected from or transmitted through an object, which is the case ASTM D2244-25 covers for opaque specimens.

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