Red-green color blindness is the most common form, followed by blue-yellow color blindness and total color blindness.
Males are at a greater risk of inheriting an X-linked mutation because males only have one X chromosome (XY, with the Y chromosome carrying altogether different genes from the X chromosome), and females have two (XX); if a woman inherits a normal X chromosome in addition to the one that carries the mutation, she will not display the mutation. Men do not have a second X chromosome to override the chromosome that carries the mutation.
Ishihara Plate No. 1, presented here in black and white so that even the fully colorblind get a sense of how the test works. Look for the number represented by dots of a different color as they shift from black through grey to white.
Designers need to take into account that color-blindness is highly sensitive to differences in material. For example, a red-green colorblind person who is incapable of distinguishing colors on a map printed on paper may have no such difficulty when viewing the map on a computer screen or television. In addition, some color blind people find it easier to distinguish problem colors on artificial materials, such as plastic or in acrylic paints, than on natural materials, such as paper or wood. Third, for some color blind people, color can only be distinguished if there is a sufficient “mass” of color: thin lines might appear black, while a thicker line of the same color can be perceived as having color.
Designers should also note that red-blue and yellow-blue color combinations are generally safe. So instead of the ever-popular “red means bad and green means good” system, using these combinations can lead to a much higher ability to use color coding effectively. This will still cause problems for those with monochromatic color blindness, but it is still something worth considering.
When the need to process visual information as rapidly as possible arises, for example in an emergency situation, the visual system may operate only in shades of gray, with the extra information load in adding color being dropped.
Some tentative evidence finds that color blind people are better at penetrating certain color camouflages. Such findings may give an evolutionary reason for the high rate of red–green color blindness. There is also a study suggesting that people with some types of color blindness can distinguish colors that people with normal color vision are not able to distinguish. In World War II, color blind observers were used to penetrate camouflage.