Careful measurements of our visual system’s best performance have been
made by psychophysicists (people who study human responses, like seeing
color, to things in the world, like light). They have shown that we can see
about 1000 levels of light-dark, 100 levels of red-green, and 100 levels of
yellow-blue for a single viewing condition in a laboratory. This means that
the total number of colors we can see is about 1000 x 100 x 100 = 10,000,000
(10 million). A computer displays about 16.8 million colors to create fullcolor
pictures, really more than necessary for most situations.
However, the answer is not quite so simple. What color looks like is greatly
affected by the viewing conditions. These conditions include the color of
the lighting, the amount of lighting, and other colors in the scene. Colors
also appear in different modes when they appear on different objects such
as surfaces, light sources, or within volumes. Different people also have
slight differences in the way they see color.
Since we can see at least 10-million colors in a single viewing condition and
the variety of viewing conditions and observers is endless, then the only
truly correct answer is infinity. If we have 10-million colors, times 10-
million lighting types, times 10-million lighting levels, times 10-million
surrounding colors, times 6-billion people in the world, times 3 modes of
viewing we get a really huge number. The result of that multiplication is 18
followed by 33 zeros (18,000,000,000,000,000,000,000,000,000,000,000), or 18
decillion. That might not quite be infinity, but is close enough since all
those estimated numbers are probably on the low side. And there is no way
to exactly measure each of them
