Colour Blindness

Inability or reduced ability to see colours/colour differences under normal light conditions.
About 8% of men and 0.4% of women suffer.
Most common in red-green area.
Complete colour blindness resulting in only black & white affects only 0.00001% of both genders.
Mostly an inconvenience. Can be restrictive, i.e. aircraft pilots need perfect colour vision.
Consider colour blindness when defining colour scheme for web sites, especially text on background.