Diamonds are not all truly colorless. Truly colorless diamonds are quite rare. Most diamonds are nearly colorless with faint yellow or brown tints.

A lettering system from D to Z is used to identify the amount of color present in a diamond, with D awarded only to the rare, totally colorless stone.

Fluorescence

For reasons not entirely understood, certain diamonds emit a subtle blue glow when exposed to ultraviolet rays. This interesting phenomenon is called fluorescence. Many light sources including the sun, fluorescent office lights, and "black" lights emit ultraviolet rays. In normal lighting conditions, fluorescence cannot be seen.

The appearance of fluorescence in diamonds exposed to strong ultraviolet lamps ranges from very faint (barely perceptible) to very strong (a neon-blue glow). Some diamonds show no fluorescence at all.

With few exceptions, fluorescence in diamonds affects neither price nor appearance. There are two exceptions to this rule.

In a minute number of cases, diamonds with very strong fluorescence and a special arrangement of clarity characteristics may look slightly "cloudy," but consumers rarely encounter such diamonds.

Fluorescence may also have a slightly positive influence on the appearance of certain off-colored diamonds, thereby making them more desirable to own.

Diamond Color Grades

Diamonds are graded by their relative lack of color. A diamond that is said to have "fine color" has little or no coloration. The less the color, the higher the value.

D-E-F

Colorless.

G-H-I-J

Nearly colorless.

K-L-M

Faintly tinted, usually yellow.

N-O-P-Q-R

Lightly tinted, usually yellow. Tint can be seen with the naked eye.

S-T-U-V-W-X-Y-Z

Tinted, usually yellow. Tint visible to the naked eye.