There are two categories: colorless and fancy. Colorless diamonds are graded on a universal scale from D (completely clear) to Z (traces of yellow, gray, and brown), with a letter grade for each shade. While D color is like looking into a piece of glass, "E and F are also in the colorless range, and G through J are near colorless," explains Moses. "After K or L, colors start to turn very light yellow." Completely colorless stones are typically the rarest and most expensive on this scale, but some consumers actually prefer the look of a slightly warmer (or even very warm) white. For that reason, most diamonds sold in jewelry stores lie in the D to L range, as variations can be indiscernible to the untrained eye, and choosing a stone often falls to personal reference.
Fancy diamonds (yellow, pink, blue, and other naturally colored stones) are rarer, often putting them at a higher price point than colorless ones. They are graded on their own scale; a more saturated shade is generally a more expensive stone.