Approximately 9% of males and less than ½% of females have some form of color perception problem. While they are typically called color blind, a complete inability to see any color is extremely rare. Here is a summary of the various forms of color blindness and how common they are.

By far, the most common problem is red-green color blindness (or reduced red-green distinctions). This problem makes virtually all color perception inaccurate, not just pure hues of red and green. Reds, oranges, yellows, and greens all tend to look yellow and all blues and purples look blue. The following images have been altered to simulate what protanopes and deuteranopes see.

Original image
Protanopia	Deuteranopia

Color perception problems are typically diagnosed using the Ishihara color vision test, developed by Dr. Shinobu Ishihara. The test involves showing the patient several pictures consisting of multicolored dots. A person with proper color vision will see a number within the dots and tells the test administrator what the number is. Color blind individuals will see only dots, or will see a different number than what normal individuals see. The discontinuity and varied darkness of each dot helps elliminate secondary clues that might hint at what the number is.

Ishihara plate example (left). Normally sighted people will see the number seven among the dots. Red-green color blind people will see nothing but random dots (right).

Sample image: Detail of "The Holy Trinity," painted by El Greco in 1577.