The color of a diamond depends on impurities and defects in its structure, natural radiation exposure. The color may be uneven - spots or patches. Sometimes in one diamond, you can see several colors at once.
Most diamonds are colorless with slight shades of pale yellow, yellow, and brown of varying intensity. Less common are greenish, bluish, mauve, ruby red, and blue stones.
The most highly prized are colorless diamonds of "pure water", that is, absolutely transparent, without any shade. Pure stones with a bluish tint are no less popular. Rare sapphire blue diamonds are also very expensive.
Most countries use the GIA diamond grading system to determine the color. Colors in it are designated by letters from D (completely colorless) to Z (with a pale yellow or brown tint). In post-Soviet countries, colors are indicated by numbers from 1 (colorless) to 9 (brown).