The colour of a diamond has a significant impact on its value. The rarest diamonds have no trace of colour at all. These are extremely uncommon as most diamonds have a slight trace of colour be it yellow or brown.

The colour scale ranges from D to Z, from colourless to light yellow, respectively. The farther from colourless that a diamond's grade is, the less rare and therefore less valuable it is.

When buying a diamond, take into consideration that it is often very difficult to detect the difference between a colourless diamond (D-F) and a near colourless diamond (G-H), especially when it is mounted in jewellery. Diamonds with a J colour grade usually have yellow shading that can be detected by the naked eye. However, a well cut stone with good proportions will still release the brilliance and fire of a lower coloured diamond, dispersing light in such a way that it lends to a beautiful stone.

If you can afford it choose a colourless diamond with a grade of D- F.
For excellent value choose a diamond with no noticeable colour to the unaided eye with a grade of G - I.

Diamonds also come in a range of natural fancy tones, such as blue, pink, green, and red. Such diamonds have so much colour that they are not graded on the normal scale D-Z. Believe it or not, these fancy diamonds are particularly rare, and like their colourless counterparts, can also come attached to a high price tag. Bear in mind that colour does not have an exclusive impact on a diamond's value. The value of a stone is affected by a combination of qualities including shape, clarity, cut, and carat weight, as well as its colour.

Though fancy coloured diamonds occur rarely in nature, with modern science they can occur quite readily in a laboratory . Irradiated diamonds are natural colourless diamonds that have been treated with a special combination of radiation and intense heating to colour the stone. The treatment creates a permanent colour change, and leaves no harmful traces of radiation on the diamond. Even though they are still real diamonds, irradiated fancy coloured diamonds have a lower value than naturally occurring fancy coloured diamonds. They can be detected though using spectroscopic analysis .

D, E, F: Colourless.

G, H, I: Near colourless. Only a trained eye can identify a trace of colour.

K, L, M: Slight yellow colour visible to the untrained eye.

N, O, P, Q, R: More yellow noticeable to the untrained eye.

S to Z: Obvious yellow colour to the untrained eye.