Color Blindness

Color blindness is a medical condition that causes people to have difficulties or be unable to discern different colors. This problem occurs due to defects in the cones, the nerve cells of the eye that detect color. When this malfunction occurs in one pigment, it becomes difficult to tell the difference between two different colors, most commonly red and green. To people with this condition, red and green will appear similar, and as a brown or brownish yellow. It is also possible for a person to be blue/green colorblind; they would have trouble discerning blues, greens and yellows. Although rare, it is possible for a person to be completely color blind; they can see no color at all. Color blindness can be passed down genetically or be caused by damage to the eye, optic nerve or optic centers of the brain, or fail with age. There is no known cure. It is estimated that 8% of the male global population are color blind, while only .5% of women are affected.

About Color Blindness
Color blindness can both be inherited genetically and caused by physical or chemical damage to one’s eye, optic nerve, or parts of your brain that process color. Even old age can contribute to a loss of color vision. Inherited color blindness is caused by abnormal photo pigments (color-detecting molecules) formed in cone-shaped cells in the retina. Defects in the genes needed for the body to make working photo pigments lead to color blindness. There are three different types of color blindness. This is because there are three types of cone cells in your retina with photo pigments—one that responds to red light, one to green light, and one to blue light. Color blindness is caused by a deficiency in photo pigments in one of the cones. The three types of color blindness are Red-Green Color blindness, Blue-Yellow color blindness, and complete color blindness.


 * Red-Green Color Blindness is the most common color blindness. It is caused when either the red or green photo pigments are abnormal or there are no working red or green cone cells.
 * Blue-Yellow Color Blindness is a less common color blindness. This is caused by the cone cells that respond to blue have abnormal photo pigments or are malfunctioning.
 * Complete Color Blindness is extremely rare. With this color blindness, you see the world in black, white, and grey. This is where at least 2 of the 3 cone-cells in the retina have abnormal or malfunctioning photopigments.

Color Blindness is genetically passed down on the X chromosome, causing more men to be affected than women.

Color Blindness in Map Design
Color blindness must be considered in map design and can affect it in two ways.


 * 1) A color blind cartographer
 * 2) A color blind audience

The Color Blind Cartographer
The color blind cartographer should be aware of the extent and type of color blindness they experience. There are a number of free online tests that vary in reliability (see ) but visiting an optometrist is recommended for an accurate diagnosis.

The Color Blind Audience
For color blind viewers, cartographers should consider their color palettes when designing maps. Lighter, pastel colors are more confusing and will be harder for a color blind user to interpret than darker colors. Maps that use a red to green or blue to purple color scheme also have a greater chance of being misinterpreted because it is so difficult for the color blind to differentiate between those color pairs.

Methods used by cartographers to limit the effects of colorblindness include using a combination of symbols and colors to limit the proximity of colors that may appear confusing to a color blind person (i.e. red and green; blue and purple). Ultimately, cartographers can use certain color schemes that are easier for color blind people to interpret.

Aids to Mapping for Color Blindness
Cartographers who deal with color blindness can use a variety of methods to "proof" their maps before publishing them. Peer review by a non-color blind individual can help identify any confusion the colors may cause and limit misinterpretation among all viewers. Corrective lenses or glasses that specifically target color blindness are available, in addition to filters that can be added to a computer screen or map to detect areas of confusion for other cartographers and viewers.

Websites that simulate the way graphics would be seen by the color blind are available. A few of these include:
 * Vischeck[http://www.vischeck.com/
 * Color Oracle[http://colororacle.org/
 * Color Brewer[http://colorbrewer2.org/.

You can load your own images and maps into their format and these programs will not only depict their colorblindness but discern whether they are colorblind safe or not. Color Brewer also provides 35 different color schemes that would would work for various classes of color blind individuals. There are 18 sequential, 9 diverging, and 8 qualitative schemes available.