Color or
colour (see
spelling differences) is the
visual perceptual property corresponding in
humans to the categories called
red,
blue,
yellow,
green and others. Color derives from the
spectrum of light (distribution of
light power versus
wavelength) interacting in the eye with the spectral sensitivities of the
light receptors. Color categories and physical specifications of color are also associated with objects, materials, light sources, etc., based on their physical properties such as light absorption, reflection, or emission spectra. By defining a
color space, colors can be identified numerically by their coordinates.
Because perception of color stems from the varying
spectral sensitivity of different types of
cone cells in the
retina to different parts of the spectrum, colors may be defined and quantified by the degree to which they stimulate these cells. These physical or
physiological quantifications of color, however, do not fully explain the
psychophysical perception of color appearance.