Diamonds occur in every color of the spectrum, and the most popular are colorless. Laboratories, such as the Gemological Institute of America (GIA) and European Gemological Laboratory (EGL), will grade diamonds based on their deviation from the purest white using an alphabetical scale beginning with the letter D. Colorless diamonds are graded D-F and near-colorless G-J. Diamonds graded K and lower will have a warm yellow or brown tint. Although most diamonds come in shades of white, yellow and brown, they are also found in red, pink, canary yellow, blue and purple. These are known as Fancies and are graded by the intensity of the color. This scale is Faint, Very Light, Light, Fancy Light, Fancy Intense, Fancy Vivid, Fancy Dark and Fancy Deep. These fancy-colored diamonds are extremely rare and the most valuable of all.
Why does the GIA color grading system start at D?
Before GIA universalized the D-to-Z Color Grading Scale, a variety of other systems were used loosely, from A, B and C (used without clear definition), to Arabic (0, 1, 2, 3) and Roman (I, II, III) numerals, to descriptive terms such as "gem blue" or "blue white," which are notorious for misinterpretation. So the creators of the GIA Color Scale wanted to start fresh, without any association with earlier systems. Thus, the GIA scale starts at the letter D. Very few people still cling to other grading systems, and no other system has the clarity and universal acceptance of the GIA scale.
Are Zs considered
No. Naturally colored diamonds outside the normal color range are called fancy-color diamonds. The FTC provides no guidelines for the use of the term “fancy-color” in the US, but there is a general agreement in the international trade that fancy-color diamonds are either yellow or brown diamonds that have more color than a Z masterstone or they exhibit a color other than yellow or brown.