A colour model developed by the CIE and based on a standard observer whose colour vision is representative of the human population having normal colour vision. The first CIE colour model was published in 1931. A colour is specified by a triad of numbers (X,Y,Z). These tristimulus values give the amount of each of three hypothetical supersaturated primaries in the colour. The Y value gives the luminance of the object and the primaries are chosen such that the perceptible colours are defined by positive values.

In 1964, the model was updated and based on data with a wider viewing angle and correcting the Y primary, which was found to be slightly in error. Two new specifications, CIELAB and CIELUV, were defined in 1976. The CIELAB model represents colours on subtractive media, where light is absorbed by inks, dyes, and other pigments; the CIELUV model represents colours on additive colour media such as emissive phosphor displays and coloured lights. The lightness scale for both is the same and is based on the cube root of luminance, which gives a linear scale.