It is in every GISer’s best interest to have an understanding of what color deficiency
is, how to design around it, and how to check a map to make sure it is readable.
So first let’s focus on what color deficiency is. The term describes a whole
range of deficiencies that range from mild inability to distinguish a few colors to
the very rare inability to see any colors except black and white. The most common
deficiency is red–green, which causes both red and green colors to appear brown.
Red–green deficiency is (usually) a genetic condition that affects about 8 percent of
men and 0.5 percent of women of Northern European descent. The rates are much
lower in other populations: about 5 percent of Asian males and about 4 percent of
African males, for example. A rarer deficiency is the inability to distinguish between
blue and yellow. The blue–yellow deficiency appears in the same proportion of men
as women but affects only about 0.01 percent of all people. The rarest deficiency is
black–white, which affects only about 0.003 percent of all peo