While many diamonds appear colorless, many actually have subtle yellow or brown tones visible under proper lighting. The color of diamonds range from Colorless through Near Colorless, Faint Yellow and Very Light Yellow.

Using the alphabet, GIA began its Colorless - Yellow grading scale with the letter D and going down through the alphabet to letter Z. They started from D simply because many wholesalers already used A, B and C to describe the quality of their diamonds.

The grading is done by comparing each diamond to a set of master-stones, which have already been verified by the GIA. True colorless diamonds are treasured for their rarity, but beautiful diamonds are also found in the near-colorless range as well. Most diamond engagement rings are sold in the colorless and near-colorless range, which would include color grades from D through J.