How should I design color for dichromats?
Dichromats are 1% of the population. Moreover, rod activation gives at least some dichromats the ability to perform some red-green color discrimination. In fact, studies find that dichromats generally use the same 11 basic color terms are trichromats. If the designer wishes to take dichromats into account, the usual advice is to chose colors which differ greatly in brightness. This is called redundant coding – covarying two or more perceptual dimensions so that a viewer can use either to perform the task. Many advocate starting with black and white and then adding color after the design is complete. In this scheme, the designer substitutes chromatic colors with similar brightness to the achromatic colors in the image. The strategy for mapping from chromatic to achromatic colors can be based on the rough categorization into four brightness classes.
