Though diamonds come in a wide range of colors, colorless diamonds have traditionally been considered the most valuable. Most diamonds are graded on a scale using the letters of the alphabet, from D (colorless), the best grade, through Z. It is difficult for the untrained eye to notice such variations in color unless stones are being compared side by side.
The comparatively rare colored diamonds are known as fancy-colored and are also quite valuable. They range in hue from the more common yellow to pink, blue, green, red, and even black and white.
Diamonds that are graded D, E, and F tend to be the most expensive because of their rarity. Diamonds graded below J are not recommended for engagement rings. However, any diamond you buy should have a good balance of cut, color, and clarity, so as to impart the most brilliance and dazzle possible.