A set of primary colors is a small, arbitrary set of pigmented physical media, lights or purely abstract elements of a mathematical colorspace model. Distinct colors from a larger gamut can be specified in terms of a mixture of primary colors which facilitates technological applications such as painting, electronic displays and printing. Any small set of pigments or lights are "imperfect" physical primary colors in that they cannot be mixed to yield all possible colors that can be perceived by the human color vision system. The abstract (or "imaginary") primaries X, Y and Z of the CIEXYZ colorspace can be mathematically summed to specify essentially all colors that can be perceived but these primaries cannot be physically realized due to the underlying structure and overlapping spectral sensitivities of each of the human cone photoreceptors. The precise set of primary colors that are used in a specific color application depend on gamut requirements as well as application-specific constraints such as cost, power consumption, lightfastness, mixing behavior etc. In an additive set of colors, as in coincident projected lights or in electronic visual displays, the primary colors normally used are red, green and blue (but the precise visible light spectra for each color can vary significantly). In a subtractive set of colors, as in mixing of pigments or dyes for printing, the colors magenta, yellow and cyan are normally used. See RGB color model, and CMYK color model for more on these popular sets of primary colors.

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