Contrast and attention to color combinations will help pages be more readable for people who suffer from color blindnesss also known as color deficiency. The most common deficiency is the red-green combination (see color wheels below).
The following graphics and more detailed information can be found at Color Blind, by Dr. Terrance Waggoner
Red-green color blindness is the most common type of color deficiency. What a color blind person sees all depends on whether they have difficulty seeing green or seeing red.
Protanope Color Blind - "red-weakness"
Normal Color Circle
Deuteranope Color Blind - "green-weakness"
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