In painting apps, color gradients are calculated within abstract color models, apparently without any particular care for how humans see or what humans expect. If you've ever felt you could see "Photoshop colors" in the dull and stodgy hues of a digitally-colored comic book or illustration, it might well have something to do with that. Mixbox sets out to solve the problem by emulating the way pigments mix in real life.
Mixbox is a practical library for paint-like color mixing
Treats colors as pigments using Kubelka & Munk
Packed in a simple RGB-in, RGB-out interface
Available in C++, Python, GLSL and more
I vaguely remember someone (game design legend Bennett Foddy?) trying to explain the gradient problem to Photoshop folks and finding it very difficult to overcome their faith in straight lines through mathematical color spaces.
