Color
Diamond color is all about what you can't see. Diamonds are valued by how closely they approach colorlessness - the less color, the higher their value. (The exception to this is fancy-color diamonds, such as pinks, blues and bright yellows, which lie outside this color range.)
The GIA Color Scale extends from D (colorless) to Z (light yellow or brown). Truly colorless (D) diamonds are very rare, and most diamonds used in jewelry are nearly colorless.
Color grades are determined by comparing each diamond to a master set. Each letter grade represents a range of color and is a measure of how noticeable a color is. Many of these color distinctions are so subtle as to be invisible to the untrained eye. But these slight differences make a very big difference in diamond quality and price.