Colour

Colour is the visual perceptual property corresponding in humans to the categories called red, blue, yellow, etc. Colour derives from the spectrum of light (distribution of light power versus wavelength) interacting in the eye with the spectral sensitivities of the light receptors. Colour categories and physical specifications of colour are also associated with objects or materials based on their physical properties such as light absorption, reflection, or emission spectra. By defining a colour space colours can be identified numerically by their coordinates.

Because perception of colour stems from the varying spectral sensitivity of different types of cone cells in the retina to different parts of the spectrum, colours may be defined and quantified by the degree to which they stimulate these cells. These physical or physiological quantifications of colours, however, do not fully explain the psychophysical perception of colour appearance.

The science of colour is sometimes called chromatics, colorimetry, or simply colour science. It includes the perception of colour by the human eye and brain, the origin of color in materials, colour theory in art, and the physics of electromagnetic radiation in the visible range (that is, what we commonly refer to simply as light).