What Is Metamerism? Definition, Meaning, and Why It Matters in Color Matching

Metamerism is a critical concept in color science and color quality control. It happens when two objects appear to match under one light source but look different under another. For professionals working in textiles, plastics, paint, coatings, cosmetics, and other color-critical industries, understanding metamerism is essential for achieving consistent color across products, environments, and the supply chain.

Metamerism Definition

Metamerism is the phenomenon in which two colors appear to match under one lighting condition but no longer match when the lighting changes. These two samples are called a metameric pair.

In simple terms, metameric objects can look the same under one illuminant even though their spectral reflectance curves are different. Once the light source changes, those spectral differences become visible, and the color match breaks down.

Example 1

What Is Metamerism in Color Science?

In color science, metamerism is understood within the framework of the CIE colorimetric system, which is based on three components:

• Light source — the illuminant shining on the object.
• Object — the sample reflecting or transmitting light.
• Observer — the person or standard observer evaluating the color.

The interaction of these three elements determines how color is perceived. This is why a color match cannot be evaluated by looking at the sample alone. Lighting conditions and observer conditions also affect the final result.

Color can be mathematically described using CIE tristimulus values, which are calculated from:

• Standard illuminants such as D65, A, or F2.
• Spectrophotometric measurement data.
• Standard observer data such as 1931 2° or 1964 10°.

What Is a Metamer?

A metamer is one of two samples that form a metameric pair.

Two samples are metamers when they appear to be the same color under one viewing condition but differ under another.

This is one of the reasons why visual approval under a single light source is not always enough for reliable color quality control.

Metamerism Meaning in Practice

The meaning of metamerism becomes especially important in production environments where color consistency matters across different locations and lighting conditions.

A color match approved in the lab may fail:

• In a retail store.
• In daylight.
• Under office lighting.
• At a customer site.
• Across different materials or substrates.

That makes metamerism a practical quality issue, not just a theoretical one.

“Controlling metamerism plays a big role in ensuring product quality. A true measure of excellence in color management is maintaining consistency, and part of that is addressing metamerism.”

Difference Between Metamerism and Color Inconstancy

Metamerism and color inconstancy are related, but they are not the same.

Metamerism

Metamerism occurs when two different samples look the same under one light source but different under another.

Color Inconstancy

Color inconstancy refers to how one single color changes appearance under different lighting conditions.

So the difference is simple:

• Metamerism compares two samples.
• Color inconstancy describes how one sample changes.

A sample with strong color inconstancy may appear unstable across lighting environments. This is sometimes described as flare. The less a color flares, the greater its color constancy.

Example 2

Learn More Terms Surrounding Metamerism

Types of Metamerism

There are several forms of metamerism that color professionals should understand.

Illuminant Metamerism

This happens when two samples match under one light source but not under another.

This is the most common type of metamerism in manufacturing and color approval workflows.

Observer Metamerism

This happens when two samples appear to match for one observer but not for another. It can occur when different standard observers are used, or when individuals perceive color differently.

Geometric Metamerism

This is a special form of observer metamerism that occurs when the viewing angle changes. It is especially common with:

• Metallic finishes.
• Pearlescent materials.
• Carpets.
• Textured fabrics.
• Directional surfaces.

Metamerism in Practice

Metamerism is especially relevant in industries where tight color tolerances are required, including:

• Textiles and apparel.
• Paint and coatings.
• Plastics.
• Cosmetics.
• Consumer goods.
• Automotive materials.

For example, synthetic materials such as acrylic yarns may show strong metameric behavior under different illuminants. A product may appear to match under the primary light source used for approval, but fail when viewed in daylight or retail lighting.

This is why color approval should not rely on one lighting condition alone.

How to Test for Metamerism

Testing for metamerism is essential when color accuracy and consistency matter.

Visual Testing

Visual testing is performed by viewing samples under multiple light sources in a controlled environment, such as a light booth.

If two samples match under one light source but not under others, they are metameric. Checking under a third light source can help confirm the result.

Instrumental Testing

Instrumental testing uses a spectrophotometer to measure samples under different illuminant and observer conditions.

This allows color professionals to:

• Compare spectral curves.
• Identify metameric pairs.
• Calculate color differences under multiple conditions.
• Quantify the degree of metamerism.

In practice, both instrumental and visual testing are important, but visual assessment often remains the final approval step.

Example 3

How Metamerism Is Quantified

Even when metamerism cannot be completely avoided, it can still be measured and managed. Several indices are used to quantify the degree of metamerism.

Common Metamerism Indices

• CIE Special Metamerism Index
• DIN 6172 Metamerism Index
• Nimeroff Index of Metamerism
• Weighted Nimeroff Index
• Root Mean Square (RMS)

These methods help color professionals evaluate how strongly a color match may shift under different illuminants or observer conditions.

How to Control Metamerism

Metamerism can be reduced with the right combination of measurement, formulation, and visual evaluation tools.

Use Spectrophotometric Measurement

A spectrophotometer helps identify spectral differences that may not be visible under a single light source.

Evaluate Colors Under Multiple Illuminants

Testing under different lighting conditions helps identify metameric risk before production.

Use Color Formulation Software

Color formulation tools can help create recipes that reduce metamerism by taking lighting and observer conditions into account.

Use Quality Control Software

Quality control software can calculate a metamerism index and flag potentially metameric pairs early in the workflow.

Use a Light Booth for Visual Assessment

A controlled viewing environment is essential for confirming how colors behave in real-world lighting conditions.

Together, these tools help reduce color approval errors, improve consistency, and lower the risk of costly production issues.

Why Metamerism Matters

Metamerism is not just a technical color science term. It directly affects product quality, customer satisfaction, and brand consistency.

If metamerism is not controlled, products that appear acceptable during development may fail later in stores, in daylight, or when combined with coordinating materials. That can lead to:

• Rejected batches.
• Rework.
• Customer complaints.
• Inconsistent product appearance.
• Higher production costs.

Understanding metamerism helps teams make better color decisions before those issues happen.

Mastering Metamerism

To manage color successfully, you need more than a visual match under one light source. You need to understand how color behaves across lighting conditions, observers, materials, and production environments.

By understanding what metamerism is, how to test for it, and how to control it, color professionals can improve color consistency and make more reliable approval decisions across the supply chain.

Talk to a Color Expert

Need help controlling metamerism in your color workflow? Datacolor’s color experts can help you choose the right combination of instruments, software, and visual evaluation tools for your application.

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