Foreground (text) against background colours must provide enough contrast to allow colour blind users or those using a monochrome screen to view information. A good contrast checking tool is WCAG Contrast checker (Firefox extension). See also: Waterloo Colour Palette for Accessibility.
On the Colour Blind Awareness site you can experience what it’s like to be colour blind. On the Vischeck site you can see what your images look like to someone who is colour blind. Roughly 1 in 20 people have some sort of color vision deficiency.
How common is color vision deficiency?
Roughly 1 in 20 people have some sort of color vision deficiency.
Red-green color vision defects are the most common form of color vision deficiency. This condition affects males much more often than females. Among populations with Northern European ancestry, it occurs in about 1 in 12 males and 1 in 200 females. Red-green color vision defects have a lower incidence in almost all other populations studied.
Blue-yellow color vision defects affect males and females equally. This condition occurs in fewer than 1 in 10,000 people worldwide.
Blue cone monochromacy is rarer than the other forms of color vision deficiency, affecting about 1 in 100,000 people worldwide. Like red-green color vision defects, blue cone monochromacy affects males much more often than females.