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A spectral color is a color that is evoked in a typical human by a single wavelength of light in the visible spectrum, or by a relatively narrow band of wavelengths, also known as monochromatic light. Every wavelength of visible light is perceived as a spectral color, in a continuous spectrum; the colors of sufficiently close wavelengths are indistinguishable for the human eye.
The spectrum is often divided into named colors, though any division is somewhat arbitrary; the spectrum is continuous. Traditional colors in English include: red, orange, yellow, green, cyan , blue , and violet. In some other languages the ranges corresponding to color names do not necessarily agree with those in English.
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". Less commonly, "VIBGYOR" is also used for the reverse order. In modern divisions of the spectrum, indigo is often omitted and the modern word cyan is used for sky-blue.
One needs at least trichromatic color vision for there to be a distinction between spectral and non-spectral colors: trichromacy gives a possibility to perceive both hue and saturation in the chroma. In color models capable of representing spectral colors, such as CIELUV, a spectral color has the maximal saturation.