Diamonds are valued by how closely they approach colorlessness - the less color, the higher the value. Most diamonds found in jewelry stores run from colorless to near-colorless with slight hinds of yellow or brown. The only exceptions are the fancy-color diamonds that lie outside of this range. The scale begins with the letter D. Representing colorless, and continues with increasing presence of color to the letter Z, or near-colorless.
Diamonds that range from colorless to light yellow and light brown fall within the normal color range. It's also called the D-to-Z range because the letters assigned to the GIA color-grading scale. The GIA color Scale begins with D (colorless) and continues through the alphabet to Z (light yellow). Within the D-to-Z range, when all other value factors are equal, colorless diamonds are the most valuable.
A diamond's color grade is based on how noticeable the color is, also known as depth of color. Because each letter in the D-to-Z scale represents a narrow color range, not a specific point, two diamonds with the same color grade can actually differ slightly in their depth of color.
the difference between one color grade and another on the GIA D-to-Z scale can have a big impact on price. the biggest jump is between the D and E grades. A 1.00ct. D Flawless diamond can cost a lot more than an E-color diamond of the same size and clarity. Further down the color scale, there's still enough of a value difference to make it important to grade color carefully and under consistent conditions.
The levels of the GIA color scale can be divided into colorless, near-colorless, faint yellow, very light yellow, and light yellow range.
Colorless (D-E-F grades)
D and E diamonds have virtually no color, and an F has a nearly undetectable amount of color that shows only in the face-down position. The difference between these grade are actually very slight. In fact, they're almost indistinguishable in diamonds smaller than 0.25ct. Diamonds in this color range are extremely rare and valuable.
Near Colorless (G-H-I-J grades)
Diamonds with these grades look colorless face-up and nearly colorless face-down. They have slight traces of color that aren't noticeable to untrained eyes when the stones are mounted. Theses diamonds are popular because they combine fairly high color with somewhat lower prices.
Faint Yellow (K-L-M grades)
Diamonds in this range show very faint yellow color face-up and face-down. When they're mounted, small stones colorless, but large ones show a slight yellow tint.
Very Light Yellow (N through R grades)
They appear very light yellow face-up and face-down, even when they're mounted in jewelry.
Light Yellow (S through Z grades)
They show substantial color face-up or face-down, loose or mounted.
Once a diamond goes beyond the Z color range, it moves into the fancy-color range, starting with Fancy Light Yellow. This causes a rise in value. Sometimes, diamond rough with color in the X to Z range can be cut to achieve a fancy-color designation.
Approximately 1/3 (35%) of all diamonds have a tendency to fluoresce when exposed to ultra-violet (UV) light. When diamonds are viewed under a UV light-source, they tend to fluoresce as blue. This fluorescent effect can be beneficial to a diamond that as a yellow tint, as the blue fluorescence will cancel out some of the yellow, making the diamond appear "colorless", but the diamond will have a dull, murky appearance when compared to a non-fluorescing diamond. Ultra-violet light is a component of natural sunlight and artificial 4800K to 5000K color-proofing light, so this effect will be more apparent under natural daylight than under artificial incandescent light.
How does Diamond Fluorescence affect price?
The impact of blue fluorescence on price depends on its notice ability. For some higher color stones, fluorescence gives the stone a milky white appearance, which greatly lower value. In some instances, the fluorescence is hardly noticeable and has minimal impact on the stone's brilliance and value. Fluorescence often adds value to lower color stones as it gives the stones a whiter, brighter appearance. Some buyers regularly pay better prices for highly fluorescent "I" color and lower stones. Yellow fluorescence may require an additional 5 to 10 percent discount. Generally, the higher the quality and price per carat the more strong fluorescence lowers value.