Diamonds that exhibit a color other than light yellow or brown, as well as diamonds that possess a more intense yellow or brown than the 'Z' color rating, are considered fancy color diamonds. With only one out of ten thousand diamonds possessing a natural color, these types of stones are extremely rare. Depending on the coloration, intensity, and hue of a diamond, color can either detract or enhance its value. Naturally occurring diamond colors include gray, white, blue, yellow, orange, red, green, olive, pink, purple, brown, and black. Red stones are the most rare of the fancy colored diamonds.
Similar to the process for grading colorless diamonds, a diamond's fancy color is graded by comparing it to master stones of predetermined color. Unlike colorless diamonds, fancy colored diamonds are graded face up. The most important factors in determining the value of a naturally colored diamond is the strength of its color. The value of a fancy colored diamond increases with the intensity of the most prominent hue within the stone.