A diamond's color is a measure of the stone's whiteness, meaning it is actually measuring the lack of color a diamond has.
The American Gem Society (AGS) has a scale to measure a diamond's color, ranging from 0.0 (colorless) to 10 (light).
D,E,F - Colorless
The rarest and most valuable diamonds, these diamonds will exhibit virtually no color when viewed by a gemologist.
G,H,I,J - Near colorless
These appear to be colorless when viewed face up by a gemologist, but will display a slight amount of color when viewed face down on a pure white background. This slight amount of color is generally not detectable to an untrained eye, especially after it has been set into a piece of jewlery.
K,L,M - Faint
Diamonds in the K-M range generally have a very faint yellow tone to them, but well cut diamonds will still
contain the brilliance and fire that make them beautiful and unique.
N,O,P,Q,R - Very Light
Diamonds in the N-R range generally have a very light yellow tone to them.
S,T,U,V,W,X - Light
Diamonds in the S-Z range generally have a yellow tone to them.
For most people, the difference between colorless, near colorless, and even the highest range of faint yellow
diamonds can be hard to see. It's actually possible for a diamond to go above a "10" color, but at that point the
diamond is re-categorized as a "Fancy Color Diamond." These extremely rare diamonds exhibit intense colors such as blue, pink, yellow green or even red and have their own set of grading parameters.