Lab
A colour space designed around human vision, with one lightness axis and two colour axes.
Also: CIELAB, L*a*b*
Lab, published in 1976 by the international lighting commission known as the CIE, describes a colour with three numbers. L is lightness from 0 to 100. The a axis runs from green to red, and the b axis from blue to yellow. It was designed so that equal steps in the numbers look like roughly equal steps to the eye, which is not true of RGB. It covers every visible colour and does not depend on any device, so it is used to measure colours, compare them and convert between other spaces.