Diamond color is simply the color that a diamond possesses. These colors often vary from colorless/clear to colorful (anywhere from pink to green, etc.) and are often used to characterize a diamond for what it's worth. In fact, according to the Gemological Institute of America (or GIA) the color of a diamond helps determine the actual value of a diamond.
The GIA created a standard scale of Colorless, Near Colorless, Faint Yellow, Very Light Yellow, and Light Yellow. D, E, F, G, H, and I represent Colorless (white). J, K, and L represent Near Colorless (white). M represents Faint Yellow (yellow). N, O, P, Q, and R represent Very Light Yellow (yellow). S, T, U, V, W, X, Y, and Z represent Light Yellow.
Going beyond the standard scale created by the GIA, there is also a Fancy which possesses a variety of colors that range from blue to pink to red to black and more, is represented as Z+. Although many diamond theorists state the actual scale starts at D, some diamond theorists have a scale that starts at A that continues to C, which represents the perfect diamond, however; that is very rare.
So, you are probably wondering, how is the actual color determined? As part of the diamond grading process where the diamond is examined by an array of professionals, a color is chosen to define that particular diamond. The color of the diamond is graded by a computer system. Is the computer system accurate? As nothing is perfect and everything is imperfect, it's definitely close to being perfect on the scale.
The color of the diamond is relevant. This is one of "the four C's" that play a very important factor and role in the actual value of the diamond.