Most gem-quality diamonds are transparent with a slight touch of nitrogen that makes them yellowish or brown. When a stone has a pronounced color, its value increases because of its rarity. We then speak of yellow canary and brown cognac.
Only a few of them have other chemical properties that offer a wider color panel. The rarest natural untreated diamonds are pink, red or blue. Black diamonds have less value.
Fancy Intense and Fancy Vivid diamonds have the highest value.