Though diamonds come in a wide range of colours, colourless diamonds have traditionally been considered the most valuable. Most diamonds are graded on a scale using the letters of the alphabet, from D (colourless), the best grade , through Z (a light yellow). It is difficult for the untrained eye to notice such variations in colour unless stones are being compared side by side.

Diamonds that are graded D, E, and F tend to be the most expensive because of their rarity. However, any diamond you buy should have a good balance of cut, colour, and clarity, so as to impart the most brilliance and dazzle possible.