PHYSICAL BASIS OF PERCEIVED COLOR

The physical basis of color exists in the interaction of light
with matter, both outside and inside the eye. The sensation
of color depends on physiological activity in the visual sys-
tem that begins with the absorption of light in photorecep-
tors located in the retina of the eye and ends with patterns
of biochemical activity in the brain. Perceived color can be
described by the color names white, gray, black, yellow,
orange, brown, red, green, blue, purple, and pink. These
11 basic color terms have unambiguous referents in all
fully developed languages. All of these names (as well as
combinations of these and many other less precisely used
nonbasic color terms) describe colors, but white, gray, and
black are excluded from the list of those called hues. Col-
ors with hue are called chromatic colors; those without are
called achromatic colors.
Although color terms are frequently used in reference
to all three aspects of color (e.g., one may speak of a sen-
sation of red, a red surface, or a red light), such usage is
scientifically appropriate only when applied to the sensa-
tion; descriptions of lights and surfaces should be provided
in physical and geometrical language.