Even the slightest change in diamond color can affect the quality and value of a diamond. Although most diamonds are thought of as colorless (that is, not fancy-colored), most colorless diamonds actually contain hints of brown and yellow. These differences in color are often very subtle –  so subtle that an untrained eye can’t tell the difference between a nearly colorless diamond and a colorless one. Yet these minute color variations can have a significant impact on the purchase price of the stone.

All non-fancy diamonds sent to GIA for grading are graded according to GIA’s internationally recognized D-to-Z color-grading scale, with D representing the top end of the scale, as a completely colorless diamond, and Z the bottom end of the scale, representing the obvious presence of a light yellow or brown hue. Each letter in the scale denotes a combination of tone (lightness or darkness) and saturation (intensity), creating a value called “depth of color.”

When GIA color graders grade a D-to-Z diamond’s color*, the diamond  is viewed table down, under highly controlled lighting conditions. It is compared to a set of carefully assembled master comparison diamonds (“master stones”) where each diamond corresponds to an alphabetical grade from D to Z.  This grading protocol ensures that the grade assigned is precisely the letter designated by GIA for that color.

Although each letter in the GIA D-to-Z color scale designates a specific color range, letters are also grouped into broader categories:

  • D through F: Colorless. These diamonds are the most chemically pure of the D to Z range.
  • G through J: Near colorless. Coloration often unseen except by trained graders. Very valuable.
  • K through M: Faint. Coloration still difficult to see by the untrained eye.
  • N through R: Very light. Coloration can be seen in larger stones by untrained eye.
  • S through Z: Light. Colorations can be seen in many sized stones. Distinctly yellow or brown but not so colored to be considered a “fancy” diamond.

Overall, the important thing to remember is that the lower the letter, the higher the grade, and the more valuable your diamond.

*Color Grading “D-to-Z”Diamonds at the GIA Laboratory, Gems & Gemology, Winter 2008