The colour of a diamond is one of the four Cs of diamond grading.

Although we usually think of diamonds as being clear or colourless, few are totally free of any tint. Normally here are minute impurities in the stone that give it a slight yellow-brown tinge, often invisible to the untrained naked eye.

Diamonds are graded on how close they are to perfectly clear. The standard colour rating system runs from D (best) to Z (worst) with diamonds graded D, E or F called “colourless”. Once you get down to grade N or below then the tint is often visible to the naked eye. As you might expect, colourless or near colourless diamonds are the rarest and – all other things being equal – the most expensive to buy.

There are times when a coloured hue is actually desirable in a diamond. As well as “white” (colourless) diamonds there is a large market for vivid, fancy coloured stones. You can buy these in a wide variety of different colours, including yellow, pink and blue, some of which are so rare as to hardly ever be seen. You can even buy chocolate and black diamonds (carbonado).

With a fancy coloured diamond a strong hue is usually better. Which colours are more valuable depends on both rarity and fashion.

Today there are various technological processes that can colour a diamond – such artificially enhanced stones are usually less valuable than their natural counterparts.