Diamonds can have different colors ranging from colorless (also called white), through yellow, blue, green, pink, orange, and to the rarest, red. The color of a diamond is determined by the chemical impurities as well as structural imperfections of the stone. Some diamond colors add to their value, often significantly. (Red diamonds are substantially more expensive than white ones—due to their rarity and natural beauty.) The least expensive are yellowish diamonds, unless the stone is a very bright yellow, making it a more valuable fancy stone.
Gemstone associations and institutes, such as GIA (the Gemological Institute of America), AGS (American Gem Society), EGL (European Gemological Laboratory), IGI (International Gemological Institute), AGA (American Gem Appraisers), etc., all have their own color grading standards and nomenclature.
The most widely used grading system was developed by the GIA. It grades diamonds from D (colorless) to M (faint yellow) all the way to Z (light yellow). Color grades beyond Z are considered to be fancy grades and are graded separately. Such diamonds are also typically more, not less, expensive than those with the yellowish hue due to their rarity and beauty.
When buying a diamond with a slightly yellow hue, tricks of the trade can help you mask some of that yellowish color. For instance, match the stone color to the setting’s metal color. Yellow metal (such as yellow gold) makes slightly yellow or brown diamonds appear more colorless, while darker yellows and browns look darker and richer. White metal makes slightly yellow or brown stones look more yellow or brown (typically in an unpleasant sort of way) but enhances the color of blue stones. So, if you go for a diamond below K-color grade (GIA grading classification), think about buying a yellow gold setting, rather than white gold or platinum.