Spectral color

The CIE xy chromaticity diagram. The spectral colors are the horseshoe shape curve on the outside. All other colors are not spectral: the bottom straight line is the line of purples, while the interior are unsaturated colors: a mixture of a spectral color and a grayscale color.

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 shade of blue/violet, and cyan was 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.

Non-spectral colors

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

• Grayscale colors, such as White, Gray, and Black
• Any color obtained by mixing a gray-scale color and a spectral color
• Purple (similarly, magenta), which is a mixture of blue and red.

See also

• Imaginary color

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