Three-dimensional, approximately uniform colour space produced by plotting in rectangular coordinated L*, u*, v* quantities defined by the following equations. Y, u', v' describe the colour stimulus considered, and Yn, u'n, v'n describe a specified white achromatic stimulus (white reference). The coordinates of the associated chromaticity diagram are u' and v'. L* is the approximate correlation of lightness, u* and v* are used to calculate an approximate correlate of chroma. Equal distances in the colour space represent approximately equal colour differences.