The numerical difference between any two colors is called Delta E (ΔE or dE).

Individual colors are not distributed linearly across a color space. When the dE of two colors is computed by simple subtraction, the same numerical value can represent a very different visual difference, depending on the region of the color space where the two colors are located. There are a number of established methods for calculating dE that apply different approaches to make the numerical differences correspond to the visual differences.

The most commonly used method for calculating dE is dE*ab, which is the default method. This method is the simplest to calculate. The other methods (dE 94, dE 2000, and dE CMC) are more complicated to calculate but are better at reflecting the visual differences between colors. The dE 2000 method is the most modern method.