A chemically pure and structurally perfect diamond has no hue like a clear window, which allows more light to pass through it than colored diamond, colorless diamonds emit more sparkle and fire. GIA's (D-to-Z) diamond color grading system measures the degree of colorlessness by comparing a store under controlled lighting and precise viewing conditions to master-stones of established color value. The D-letter represents colorless and continues with increasing presence of color till reaching the letter "Z".
Fancy color diamonds do not follow this rule, they are actually more valuable for their color. These diamonds are very rare and expensive; from blue, green, pink to yellow.
Which color grade should I choose?
Diamonds graded (D) through (F) are naturally the most valuable and most desired because of their rarity. Such diamonds are a treat for the eyes of anyone. But you can still obtain very attractive diamonds that are graded slightly less than colorless. And diamonds graded (G) through (I) show virtually no color that is visible to the untrained eye.
If your setting is white gold or platinum, you may wish to opt for a higher color grade than if the setting is yellow gold.
And while a very faint hint of yellow will be apparent in diamonds graded (J) through (M), this color can often be minimized by carefully selecting the right jewelry in which to mount your diamond. Keep in mind that, while most people strive to buy the most colorless diamond they can afford, there are many people who actually prefer the warmer glow of lower-color diamonds.