Paint color matching math works by converting each paint's color into a numeric space built around how humans actually perceive color, then measuring the distance between two paints in that space. The smaller the distance, the closer the two colors look to a person, and that distance gets turned into the similarity percentage you see on a match.
Why hex codes alone are not enough
Every paint swatch can be recorded as a hex code, a six-digit value describing its red, green, and blue components. Comparing hex codes directly seems like the obvious approach, but plain RGB math does not track human vision well. Two colors can have a large numeric RGB gap and look almost identical to the eye, or a small RGB gap and look clearly different, especially in darker shades. That mismatch is why naive color comparisons produce bad matches.
What CIEDE2000 actually does
The fix is a color difference formula called CIEDE2000, the same standard used in printing and textile industries where getting color to match consistently across materials actually matters commercially. It first converts a color from RGB into a perceptual color space, then calculates a distance value called delta E between two colors in that space. A delta E near zero means the colors are visually indistinguishable. As delta E climbs, the visible difference grows, and it grows in a way that lines up with how a person actually perceives the gap, not just how far apart the raw numbers are.
From delta E to a similarity percentage
| Delta E | What it looks like | Approximate similarity |
|---|---|---|
| 0 to 1 | Indistinguishable to the eye | 95 to 100 |
| 1 to 3 | Visible only on close side-by-side comparison | 85 to 94 |
| 3 to 6 | Clearly different colors up close | 70 to 84 |
| Above 6 | Different colors, same general family at best | Below 70 |
For example, Citadel's Mephiston Red measures a delta E of about 1.8 against Pro Acryl's Bold Pyrrole Red, which lands in the mid nineties for similarity, close enough to swap directly for most painting purposes. The same red measures a much larger delta E against paints outside its color family, and those land well below seventy.
Why this catches things eyeballing misses
A person judging color by eye is affected by the lighting in the room, the calibration of their screen or printed chart, and simple fatigue after looking at dozens of similar reds in a row. The math does not get tired and does not shift with lighting, so it produces the same result every time for the same two colors. It is not infallible, since it only knows the recorded color and nothing about finish, opacity, or how a paint handles wet, which is why finish type is always checked alongside the number.
How to use this when picking a match
Treat similarity in the mid nineties and above as safe to swap without adjustment. Treat the seventies and low eighties as a starting point that will likely need a small tweak with white or a darker shade once you see it on the model. Always confirm the finish type on the paint's page before buying, since the math cannot see whether you are comparing a metallic to a matte.
FAQ
What does delta E mean in paint matching?
Delta E is a single number representing how different two colors are in a perceptually accurate color space. Lower means more similar, with values under about 2 generally indistinguishable to the eye.
Why is CIEDE2000 used instead of simple RGB distance?
Plain RGB distance does not track human color perception accurately, especially in darker or more saturated colors, so it produces matches that look wrong in practice even when the numbers seem close.
Can the math be wrong about a match?
The math is only working from recorded hex color values, so if the underlying color data is inaccurate, the match will be too. It also cannot account for finish, which is why finish type is always checked separately.
Does a higher similarity percentage always mean a better paint swap?
For color alone, yes. For overall suitability, check the finish type and intended use as well, since a very close color match in the wrong finish class is not a usable substitute.