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 Delta E 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 Delta E that apply different approaches to make the numerical differences correspond to the visual differences.

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