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 Isaac 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; see indigo #Classification as a spectral color for details.

In HSL and HSV color models a spectral color has the maximal saturation among all colors of the same hue.

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.
• Any CMYK color.

Table of spectral or near-spectral colors

Most of colors listed do not reach the maximal (spectral) colorfulness, or are not usually seen with it, but they can be saturated enough to be perceived closely to their dominant wavelength spectral colors. Ranges of wavelengths and frequencies are only approximate. The only RGB-implemented colors which might be really spectral are its primaries: red, green, and blue.

	Color term	Sample	Wavelength, nm	Frequency, THz	Hue	Comments
	Red		740–630	405–480		A traditional, broad color term, which includes some nearby non-spectral hues
	• red (RGB)		?	?	0°
	Orange   Amber		620–585	483–512	≈ 30°
	Yellow		585–560	512–540		A traditional color term
	• yellow (NCS)		?	?	50°	Munsell yellow and gold have almost identical chroma at h = 51°
	• process (canary) yellow		?	?	56°
	• yellow (RGB)		?	?	60°
	• Chartreuse yellow		?	?	68°
	Lime		≈ 564	?	≈ 75°	May be classified as either green or yellow
	Green		560–???	540–???		A traditional, broad color term
	• Chartreuse green		?	?	90°
	• Bright green		≈ 556	?	96°
	• Harlequin		≈ 552	?	105°
	• green (RGB)		?	?	120°
	• green (NCS)		?	?	160°	Munsell green at h = 163° is nearby
	Cyan		505–480	593–624		Sometimes included (or overlaps) with blue, terminological distinction between the two is inconsistent
	• Turquoise Blue[sic]		?	?	≈ 175°	Most of "turquoise" lies far away of the spectrum
	• cyan (RGB)		?	?	180°
	• Blue[sic] of Munsell		?	?	190°
	• process cyan		?	?	193°
	Blue		490–450	610–670		A traditional, broad color term, which used to include cyan
	• Azure		≈ 488	≈ 614	≈ 210°
	• blue (RGB)		≈ 445	≈ 674	240°
	Indigo		definition is controversial
	Violet		450–400	670–750	?	As spectral, is very dim and rarely seen. The term also extends to purples

See also

• Imaginary color