SPECTRAL COLOUR

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 isRoy G. Biv. In modern divisions of the spectrum, indigo is often omitted as simply a tone of blue or violet, that is, created by the addition of grey.