Spectral color

The CIE xy chromaticity diagram. The spectral colors are the colors on the horseshoe shaped curve on the outside of the diagram. All other colors are not spectral: the bottom straight line is the line of purples, while within the interior of the diagram are unsaturated colors that are various mixtures of a spectral color or a purple color with white, a grayscale color, which is in the central part of the interior of the diagram, since when all colors of light are mixed together, they produce white.

A spectral color is a color that is evoked by a single wavelength of light in the visible spectrum, or by a relatively narrow band of wavelengths. Every wavelength of light is perceived as a spectral color, in a continuous spectrum; the colors of sufficiently close wavelengths are indistinguishable.

The spectrum is often divided up into named colors, though any division is somewhat arbitrary: the spectrum is continuous. Traditional colors include: red, orange, yellow, green, blue, and violet.

Indigo is often omitted as simply a tone of blue or violet, and the spectral colors chartreuse green, spring green, cyan, and azure were not included historically. The first division was by Newton, in his color wheel, and he used Red, Orange, Yellow, Green, Blue, Indigo and Violet; a mnemonic is ROYGBIV, as in a person named Roy G. Biv.

Non-spectral colors

Among some of the colors that are not spectral colors are:

• Grayscale (achromatic) colors, such as White, Gray, and Black
• Any color obtained by mixing a gray-scale color and a spectral color, such as coral red, which is a mixture of red and white.
• Purple colors, which in color theory also include magenta colors, rose colors, and other colors on the line of purples, which are various mixtures of blue and red light.

See also

• Imaginary color