What Is Color Difference ΔE? How to Read and Evaluate It

Understanding and Applying Color Difference ΔE

What is color difference ΔE? How do you read and evaluate it?

ΔE (Delta E) is a numerical way to express the overall difference between two colors. It is commonly used in research and development, color matching, incoming inspection, process adjustment, batch comparison, and customer acceptance. A larger ΔE usually means a larger overall color difference. To understand the direction of the difference, also look at ΔL*, Δa*, and Δb*.

Remember: ΔE tells you how different two colors are overall; ΔL*, Δa*, and Δb* tell you which direction the sample has shifted.

People may easily see that one color looks redder, yellower, darker, or lighter. But when R&D teams, suppliers, manufacturers, and customers need to compare results, visual judgment alone is difficult to communicate consistently. Color measurement therefore commonly starts with color data such as CIE L*a*b*, then uses a ΔE formula to express the overall difference between a reference and a sample.

ΔE is not a universal acceptance limit. There is no single ΔE value that applies to every product. Acceptable difference depends on the material, surface, end use, measurement conditions, and the standard agreed by the parties.

1. What is ΔE?

ΔE is a value describing the overall difference between two colors. A common workflow is to establish a reference standard, measure the sample to be compared, and calculate ΔE from the color data of the two.

This makes ΔE useful in many situations: comparing two formulations, monitoring a process change, checking different production batches, comparing incoming materials from suppliers, or confirming a product against an existing standard before delivery.

ΔE mainly answers “how much difference?” To tell whether the sample is lighter, darker, redder, greener, yellower, or bluer, check ΔL*, Δa*, and Δb* as well.

2. How are ΔE and L*a*b* related?

L*a*b* describes a color's position along three dimensions. ΔE uses the difference between the reference and sample color data to calculate one value representing the overall color difference.

L* — lightness. A change indicates whether the sample is lighter or darker.
a* — red–green direction. It indicates whether the color shifts toward red or green.
b* — yellow–blue direction. It indicates whether the color shifts toward yellow or blue.

For a fuller explanation of L*, a*, b* and ΔL*, Δa*, Δb*, see a guide to Lab values.

3. How is ΔE*ab calculated?

ΔE*ab is one commonly used expression of color difference. It calculates the three-dimensional distance between the reference and sample using their differences along ΔL*, Δa*, and Δb* in CIE L*a*b* space:

ΔE*ab = √[(ΔL*)² + (Δa*)² + (Δb*)²]

ΔL* represents the lightness difference between the reference and sample.
Δa* represents their difference along the red–green axis.
Δb* represents their difference along the yellow–blue axis.

ΔE*ab is not the only color-difference formula. Industries, customer specifications, or applications may use other formulas. Before comparing values, confirm that both parties use the same calculation method.

4. Does a smaller ΔE always mean the color is acceptable?

No. ΔE indicates the overall size of the difference, but a single number cannot determine pass or fail for every product. The ranges below help illustrate how ΔE values may relate to visual differences; they should not be treated as universal acceptance criteria for all materials or products.

ΔE* 0–1: The difference is usually small and may be difficult to distinguish by eye.
ΔE* 1–2: A slight color difference may begin to be noticeable.
ΔE* 2–3: The color difference may be easier to identify.
ΔE* 3.5–5: The difference may be more apparent.
ΔE* greater than 5: The visual difference is usually more apparent.

The important question is how much difference is acceptable for the product's actual use and inspection situation. Convert that requirement into measurement conditions and a decision standard agreed by both parties.

5. Why can the same formulation still produce different colors?

Color is affected by more than the formulation. Even when the same raw materials or formula are used, differences in material, surface, thickness, processing, or viewing conditions can change the appearance and measured result.

Material and substrate: Different materials absorb and reflect light differently, so similar formulations may look different on different substrates.

Gloss and surface texture: Glossy, matte, textured, rough, or otherwise structured surfaces change how light is reflected.

Process conditions: Coating thickness, baking, injection molding, drying, and other process changes can alter the final color.

Sample shape and measurement location: Curved, small, irregular, or nonuniform samples can produce different readings when measured at different locations.

SCI/SCE mode: On glossy samples, the selected SCI or SCE setting can affect L*a*b* and ΔE results.

Lighting and viewing conditions: Two samples that look similar under one light source may look noticeably different under another. This may be a case of metamerism.

6. Which conditions should be fixed when comparing ΔE?

When different people, departments, suppliers, and customers compare ΔE, simply saying “we all use ΔE” is not enough. Different measurement conditions can produce different values. Align the following:

Reference standard: Confirm that everyone is comparing against the same standard, and check its storage and surface condition.

Measurement location: For textured, gradient, or nonuniform samples, standardize the measurement area and positioning method.

Measurement aperture: Different apertures cover different sample areas; this matters especially for nonuniform samples.

Illuminant and observer: Confirm that the same calculation conditions are being used for comparisons.

SCI/SCE: For glossy samples, confirm that both sides use the same measurement mode.

Color-difference formula: ΔE*ab and other formulas are calculated differently and must not be mixed in a comparison.

In practice, if a customer's and supplier's ΔE results do not match, first check whether their measurement conditions are aligned before deciding that one instrument is more accurate.

7. Where is ΔE commonly used?

R&D and color matching: Compare formulations or color before and after adjustment, and use ΔL*, Δa*, and Δb* to see the direction of change.

Incoming inspection and supplier comparison: Compare incoming material with an established standard or check color consistency across suppliers.

Process adjustment: Monitor whether changes in process parameters cause the sample color to drift from the original standard.

Batch comparison and acceptance: Compare production batches or delivery samples so both parties can discuss results using consistent color data.

Should you use a colorimeter or a spectrophotometer?

ΔE can be obtained from different types of color-measurement instruments. If your question has moved from “how do I read ΔE?” to “which instrument is suitable?”, compare colorimeters and spectrophotometers based on your application.

Frequently asked questions about ΔE

Does a smaller ΔE mean the two colors are closer?
Generally, a smaller ΔE means a smaller calculated overall color difference. Actual appearance can still be affected by gloss, texture, lighting, and viewing conditions.

What ΔE is acceptable?
There is no single value that applies to every product. Establish a standard based on the material, product use, customer requirements, and the visual difference that is acceptable in practice.

Why do two instruments report different ΔE values?
Possible factors include illuminant, observer, aperture, optical design, SCI/SCE mode, reference standard, measurement location, and operating method. Align measurement conditions before comparing results.

Can ΔE alone show the direction of the color shift?
No. ΔE mainly represents the overall difference. To determine whether a sample is lighter, darker, redder, greener, yellower, or bluer, interpret ΔL*, Δa*, and Δb* as well.

Need help with a ΔE value or color measurement?
If you are comparing a reference with a sample, investigating differences between instruments, or setting up color measurement for R&D, production, incoming inspection, or acceptance, share the sample and current measurement conditions to help determine a suitable instrument and comparison method.

Contact Fulcrum Technology for colorimeters and spectrocolorimeters.