An indication of the hue, tone, and saturation of a diamond. See Color Grade.
The normal color scale, as defined by GIA:
D, E, F = Colorless
G, H, I, J = Near Colorless
K, L, M = Faint Yellow
N, O, P, Q, R = Very Light Yellow
S, T, U, V, W, X, Y, Z = Light Yellow
Some fancy colored diamonds: