"Color", the 2nd C, refers to the presence of tint within the diamond crystal. The G.I.A. Color Scale, the standard for the trade, is alphabetical, beginning at "D", which is called "colorless". The saturation of tint increases all the way down to "Z", with prices declining accordingly. The extremes of diamond color are not common, and this rarity-in-nature factor is one of the criteria that drive diamond prices. The tint in white diamonds is usually thought to be yellow, but quite often the tone may be brown or gray. Tints with color saturation beyond "Z", and those of exotic hue, are so rare, that they are called "Fancies", and also command premium prices.

"Color" is most easily seen by viewing the diamond face down through the side, against a pure white background. The stone should be viewed face down to judge tint intensity because "Cut", the most important C, can impact a diamond’s "face up" appearance. A well made stone will appear whiter than its actual tint; conversely, a poorly cut diamond can appear lower in color than its actual tint.

Tint in a diamond is not always undesirable. Many people prefer the warmth of a moderate color tone against their skin. Further, stones that possess the characteristic of fluorescence can at times enhance the perceived color, and intensify the spectral display. The G.I.A. has documented the benefits of blue fluorescence, particularly in lower color diamonds. These factors combined make Color selection a very personal decision.

Most colorless diamonds should be secured in white metal settings, usually white gold or platinum, since a diamond absorbs and reflects back the colors adjacent to it. Tinted stones can sometimes find an advantage by being set in rose or yellow gold.

Below is representation of the GIA color grading scale recognized by the international diamond trade.