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. White 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.

The division used by Newton, in his color wheel, was Red, Orange, Yellow, Green, Blue, Indigo and Violet; a mnemonic for this order is Roy G. Biv. In modern divisions of the spectrum, indigo is often omitted as simply a tone of blue or violet.

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 yet another color (either spectral one or not spectral), such as pink, which is a mixture of a reddish color 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 violet and red light.

See also

• Imaginary color