The color of a diamond refers to the quality and saturation of color, or the depth of color in a diamond. The color of a diamond can range from colorless to a yellow or brown shade. A colorless diamond is rarer and more valuable because it appears white and brighter to the eye. The most valued system used today for evaluating diamond color was developed by the Gemological Institute of America, (GIA).
Even though there are several grades in every category, there are minor differences between the letter grades. D grade is the clearest and most precious, X grade is a dirty yellow and least expensive. Z grade-colored diamonds are the rarest and most expensive. A grade diamond so drenched with nitrogen that it becomes a deep, rich yellow is as rare as a colorless diamond.