Color makes up one of the Four C's when talking about a diamonds characteristics. First time diamond buyers often come in with the assumption that all diamonds are colorless. However, the truth is that colorless diamonds are very rare. Diamonds are graded on a scale from D to Z in color.
How did the scale come about?
Before the Gemological Institute of America (GIA) came up with the D to Z scale in the 1950's, jewelry stores would label their diamonds A, B, and C or use numerical numbering systems to identify the color of their diamonds. This influenced the GIA to start their scale at D, so that customers would not confuse the GIA's color scale with any other scale. While some jewelers still use their own color scales, many people in the jewelry industry across the globe have adopted the GIA color scale to follow.
How does the scale work?
Diamonds D-F are categorized in the colorless section of the scale. G-J are classified as near colorless. K-M you can start to see faint yellow or browns in the diamond. N-R the color of yellow or brown is very light. Finally, S-Z the color is light.
How is the color determined?
When grading a diamond's color, GIA compares a set of different colored diamonds, called masterstones, to the diamond they are grading. The GIA has three gemologist compare the diamond to the masterstones and decide on a color. All three gemologist have to agree on the color of the stone for it to be graded that color.
One fun fact about diamonds is that they can come in every color (red, blue, green, and purple are just a few). These fancy-colored diamonds do not follow the same D to Z scale as regular diamonds. GIA grades colored diamonds by the intensity of their color (faint to light). Fancy-colored yellow diamonds should not be confused with a off-colored diamond that is low on the D to Z scale. Natural fancy-colored diamonds are valuable and rare to find.