Retinas have things called
cones. These are what you use to see
colors. There are three varities of cones
red,
blue, and
green. (or at least are commenly referred to as such, see
retina for more information.) The way your retinas are desensitized, or more specifically the way your cones are desensitized, is by abstaining from a certain color for some duration.
For example: I was down in my room playing
Civilization II. The
computer screen on my
computer is
messed up, and the red doesn't not come in at all. Thus when I see a
barbarian in the game, that is usually noted by a red color, it is actually black. After about an hour of not seeing red, I came upstairs and logged on to
Everything and all that had previously looked white now looks pink.
This
phenomena happens because I abstained from the red cones in the retina for a long time. In theory, if I would have seen mass amounts of red for a long duration of time then things slighty
pink would appear white.