Although most gem-quality diamonds when seen alone appear to be colorless to the untrained eye, there are subtle differences in shade which in turn affect value. Color in diamonds results from traces of other elements which mix with carbon during the diamond's formation. Diamonds with no traces of body color are extremely rare.

To determine a diamond's true color, the diamond  is viewed from the side under balanced white light. It is compared to diamonds in a "Master Set" whose colors have been predetermined by the Gemological Institute of America (GIA). All diamonds are color graded according to guidelines established by the GIA, using a Master Set and a special diamond light developed for color grading. The color grade is then assigned according to the diamond's color relative to the master set.