The GIA grades diamonds on a scale of D (colorless) through Z (light color). All D-Z diamonds are considered white, even though they contain varying degrees of color. True fancy colored diamonds (such as yellows, pinks, and blues) are graded on a separate color scale.
Below is the GIA diamond color chart with definitions:
GIA DIAMOND COLOR SCALE
D-F Diamond Color Scale
While there are differences in color between D, E, and F diamonds, they can be detected only by a gemologist in side by side comparisons, and rarely by the untrained eye.
D-F diamonds should only be set in white gold / platinum. Yellow gold reflects color, negating the diamond’s colorless effect.
G-J Diamond Color Scale
While containing traces of color, G-J diamonds are suitable for a platinum or white gold setting, which would normally betray any hint of color in a diamond.
Because I-J diamonds are more common than the higher grades, they tend to be a great value. An I-J diamond may retail for half the price of a D diamond. Within the G-J range, price tends to increase 10-20% between each diamond grade.
K-M Diamond Color Scale
Beginning with K diamonds, color (usually a yellow tint) is more easily detected by the naked eye.
Set in yellow gold, these warm colored diamonds appeal to some, and are an exceptional value. Others will feel they have too much color. Due to its perceptible color tint, a K diamond is often half the price of a G diamond.
Very Light Color
N-R Diamond Color Scale
Diamonds in the N-R color range have an easily seen yellow or brown tint, but are much less expensive than higher grades.
S-Z Diamond Color Scale
For almost all customers, S-Z diamonds have too much color for a white diamond.