The second C used in rating diamonds is color. Diamonds come in literally every color in the rainbow and while a few specialty colored diamonds are extremely valuable because of their deep hues and unique color characteristics, these are the exceptions rather than the rule. In general, the closer a stone is to possessing no color, that is, to being colorless, the more the stone is worth.
In order to establish the transparency or lack of color in a diamond, the loose stone is placed on a pure white background under a white light. There are special lights sold with adjusted color temperatures for this viewing or some people prefer to use the soft north sunlight when trying to view the color of a diamond.
The most accepted color grading system is judged by using a series of master stones that establish hues and tints and can be laid side by side with the stone in question in order to view how “white” the stone really is.
The color rating system has been established using alphabetical nomenclature. The stones are rated from pure (totally colorless) down through a sliding scale to yellow, which is the least valuable stone. The color rating system starts with the letter D and progresses through the alphabet as shown below to Z, which would be very yellow.
A B C D E F ) Colorless
G H I J ) Near Colorless
K L ) Faint
M ) Yellow-White
N O ) Very Light Yellow
P ) Light Yellow
Q ) Yellow
R S T U ) Light
V ) Yellow to Fancy
W ) Fancy
X Y Z ) Yellow
After the letter Z, indicators are used to suggest the stone is more valuable because of its hue; i.e., a “fancy” color. As you can see from the above chart, D, E and F stones are considered completely colorless. G, H, I and J are near colorless stones and take a lot of practice for the amateur to see any color at all, while after J the stones begin to pick up a small tint of yellow that is noticeable to practiced gemologists.
To correctly grade a gemstone, the stone must be loose, not in a setting, should be on a perfectly white background, should have a white gem quality temperature light and should be viewed from the rear of the stone. In other words, the stone should be upside down lying on its table. It is also extremely helpful to have stones of known color grades nearby for active comparison.
Color is a very important consideration in choosing investment quality diamonds and, in fact, the differences in large sizes such as one carat and over from a D to an E color (again these are the top rated stones and are both considered colorless to the naked eye) can be double the price between these two grades.