Diamonds appear to be colorless, but most are tinged with yellow. To help determine the proper color grading of diamonds, the Gemological Institute of America (GIA) has created a special scale. Preferred Jewelers also uses the GIA scale. The letter "D" begins the Color Grading Scale as the best example of a colorless diamond.

Color & Value
Color has a strong influence on the value of a diamond. Generally the more colorless a diamond appears, the greater its aesthetic appeal. In addition,color is the most obvious feature of the diamond's appearance after its shape. The immediate effect of the combination of color and shape is what demands our attention.

It can be generally stated that the higher the color of the diamond, the more rare is that gemstone. Indeed, truly colorless diamonds are extremely rare. It is scarcity in nature of diamonds graded "D", "E" and "F" which makes them so valuable.