Most diamonds in the world contain traces of colour. The majority are either slightly yellow or brown.

Most graders use an alphabetical scale to describe the intensity of the colour in a diamond. This scale runs from D to Z, where D is a total absense of colour, and Z is a strong tint of colour. (Stronger intensities than Z are classified as "Fancy Colours", and are a different category, both in terms or price and rarity.

Actually setting the colour grade of a diamond is a skill. You must train your eye to ignore the sparkle of the diamond, and instead look "into" the stone, to see the colour.

Here are a few tips to how to do this;

• Use non direct, natural light. Shop lights will always give a false colour, either better or worse. Direct sunlight makes it extremely difficult to grade colour.
• Try if possible to use Northern light (ie turn to the north). This ensures that the light is totally diffused and there is no direct light entering the stone.
• Use neutral background colours.Standing opposite a red-brick building, for example, may make you think that you are looking at a pink diamond!!! In the same vein, avoid wearing bright or strong colours - a bright tie, shirt or scarf can reflect into the diamond, and tint it slightly.
• Look diagonally into the diamond, focussing your eye about halfway into it. This takes a bit of practise, but soon becomes second nature.

• Use comparison stones. There can be a huge price diference between a D colour and an E colour, for example. If in doubt, compare with known standards.

Ultimately, if you are not sure, ask to see a report ("a diamond certificate") from a reputable diamond laboratory. The most widely known, and reputable, is the Gemmological Institute of America, but there are many other labs around the world of high standard.