Diamond ColourThe colour of a diamond is one of the four Cs of diamond grading and an important factor in determining the stone's price.
Although we usually think of diamonds as being clear or colourless, few are totally free of any tint. Normally there are minute impurities in the stone that give it a slight yellow- brown tinge, often invisible to the untrained naked eye. The degree of hue variation from "pure" can make a lot of difference to the price of a piece of diamond jewelry.
White"Ordinary" diamonds (usually described as "white") are colour 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.
FancyThere are times when a coloured hue is actually desirable in a diamond. As well as "white" (colourless) stones there is a large market for vivid, fancy coloured diamonds. You can buy these in a wide variety of different colours, including yellow, pink and blue, some of which are so rare in nature as to hardly ever be seen. For something completely different you can even buy chocolate and black diamonds (carbonado).
Which colours are more valuable depends on both rarity and fashion. Today there are various technological processes that can colour a diamond to almost any desired hue - such artificially enhanced stones are usually less valuable than their natural counterparts.
EnhancementWith a fancy coloured diamond a strong hue is usually better and so a number of colour enhancement processes have been developed. Colour enhancement takes many forms, from heat and pressure treatment (HPHT) to irradiation to special coatings. These treatments can either be used to remove a very faint colour tinge or to amplify a stone's natural colour to a more vivid fancy hue.
Colour enhancement should not be confused with clarity enhancement.