In general, the highest quality diamonds are totally colorless, whereas lower quality diamonds can often have a slight yellow tint. Diamond color is measured using Gemological Institute of America, or GIA color scale which goes from D (colorless) all the way to Z (light yellow or brown in color).

Heating irradiated diamonds to above 500o C will change most blue-to-green colors to brownish or orangy yellow to yellow, or, in rare cases, pink to red. High-pressure high-temperature (HPHT) annealing: Exposing diamonds to very high pressures and temperatures can lighten the color of some brownish diamonds.

In the case of Type IaA diamonds, where the nitrogen atoms are present but in pairs, and certain Type 1aB diamonds, HPHT treatment will transform brown stones into fancy yellow/orange or yellow-green stones. It does so by dispersing the paired nitrogen into single nitrogen molecules.

D color diamond is the highest grade and is extremely rare—the highest color grade that money can buy. Eight percent of customers choose a D color diamond.

Diamonds that have a clarity grade of I2 have obvious blemishes and inclusions under magnification. Some of these inclusions might even be visible to the naked eye. This diamond grade might be less sparkly than their more flawless counterparts. The buyer might notice cloudiness within the diamond’s structure.

According to that GIA standard, the “best” diamond color is D. (Read more about D color diamonds here.) D color diamonds are the equivalent of IF or FL grade diamonds on the clarity scale — they’re very rare, and their price definitely reflects that.

Technically, flawless (FL) is the best clarity of a diamond because it means the diamond does not have any inclusions or blemishes, even under 10x magnification.