Colour

colour, also spelled color, the aspect of any object that may be described in terms of hue, lightness, and saturation. In physics, colour is associated specifically with electromagnetic radiation of a certain range of wavelengths visible to the human eye. Radiation of such wavelengths constitutes that portion of the electromagnetic spectrum known as the visible spectrum—i.e., light.

Vision is obviously involved in the perception of colour. A person can see in dim light, however, without being able to distinguish colours. Only when more light is present do colours appear. Light of some critical intensity, therefore, is also necessary for colour perception. Finally, the manner in which the brain responds to visual stimuli must also be considered. Even under identical conditions, the same object may appear red to one observer and orange to another. Clearly, the perception of colour depends on vision, light, and individual interpretation, and an understanding of colour involves physics, physiology, and psychology.

Classify colors on the visible spectrum of electromagnetic radiation by hue, saturation, and brightnessSee all videos for this article

An object appears coloured because of the way it interacts with light. The analysis of this interaction and the factors that determine it are the concerns of the physics of colour. The physiology of colour involves the eye’s and the brain’s responses to light and the sensory data they produce. The psychology of colour is invoked when the mind processes visual data, compares it with information stored in memory, and interprets it as colour.

This article concentrates on the physics of colour. For an overview of the primary colours, with their basic secondary and tertiary mixtures, usefully notated as the 12 segments of a circle, see colour wheel. For a discussion of colour as a quality of light, see light and electromagnetic radiation. For the physiological aspects of colour vision, see eye: Colour vision. See also painting for a discussion of the psychological and aesthetic uses of colour.