Nearly all gem-quality diamonds are graded on a color scale that most highly values the absence of color. The most widely used color scale for grading diamonds is the D-to-Z color-grading scale developed by the Gemological Institute of America (GIA).

On the GIA scale, a grade of “D” or “colorless” is the highest grade. Traces of yellow, brown, gray, or any other color within the gem will cause it to receive a lower color grade on the D-to-Z scale.

Large Yellow Diamond Crystal: ALROSA recovered this 98.63-carat diamond with a subtle yellow color from its Jubilee Pipe in the Yakutia Region of Siberia, Russia. It measures 29 x 28 x 27 millimeters in size and is covered with interesting triangular dissolution features. This diamond is an example of a stone with a noticeable yellow color that might not have a strong enough saturation to be considered a “fancy-color diamond”. Instead it would be graded on the D-to-Z color scale as a Faint, Very Light or Light yellow color. It would make an excellent mineral specimen.

Below grade “Z” at the bottom of the GIA grading scale, a very small number of diamonds have a yellow color that is strong enough to be obvious and attractive when viewed in the face-up position.

These colored diamonds are rare and highly desirable. They are graded on a special scale according to the strength and quality of their yellow color. These diamonds are said to have a “Fancy” yellow color. On a scale developed by GIA, they are graded as Fancy Light, Fancy, Fancy Intense, Fancy Dark, Fancy Deep or Fancy Vivid according to the tone and saturation of their yellow color.