While most diamonds appear white, virtually all display barely imperceptible tints of colour. The grading of a diamond's colour measures the degree to which it approaches colourlessness. White diamonds are the most popular and the most prevalent in jewellery, but it should be noted that some highly desirable stones are coloured pink, blue, yellow or even black.
Diamonds are graded on an alphabetical scale, ranging from totally colourless, D, through to an obvious light yellow, brown or grey, Z. Initially the scale began at A, but was shortlived as confusion quickly arose when new 'unofficial' grades of A++, A+ , A- began to appear within the trade.
It should be emphasised that the differences between one grade and another are extremely subtle - even a highly trained eye will need to compare a diamond to a pre-determined set of 'master-stones', in perfect lighting, to be sure of its exact grade.
Diamonds graded D-F are considered "colourless"; these are the rarest and therefore the most expensive. Stones graded G-J are "near-colourless" and have only a slight colouration that's invisible to the naked eye. K-M diamonds are "slightly coloured" and those graded N-Y have a distinctly noticeable yellow or brown tinge.
When the strength of colour within a diamond reaches a high enough saturation, the stone will be categorized as a 'fancy' colour, as opposed to just an 'off-white' colour grade. Fancy coloured diamonds have their own grading system and attract a price premium on the principle that the colour enhances, rather than detracts from, the appearance of the stone. They are graded firstly on their basic hue e.g. pink, yellow, blue, green, etc. and secondly on the intensity of the colour. The more vivid and intense the colour the more expensive the diamond is likely to be.
The grading system used for coloured diamonds is similar to that used for other precious gemstones, such as rubies or sapphires, with each stone described using the following terms:
- Fancy Light
- Fancy Intense
- fancy vivid
You may come across this term when a diamond's quality is described, although it is not always mentioned in a grading report. Fluorescence refers to the way a stone reacts under UV light and is graded from None to Very Strong. High levels of florescence can give the stone a slightly milky or oily appearance but the affect is usually very minor. There are instances when high florescence is considered desirable.