Understanding the 4 C's - Colour

Unlocking the Mysteries of the 4 C's: Carat, Cut, Colour, and Clarity in Diamonds - By Melissa Holt DGA

When it comes to gemstones, particularly diamonds, there's a lot of talk about the famous 4 C's: Carat, Cut, Colour, and Clarity. These four aspects are the fundamental criteria used to grade and evaluate diamonds, and they were introduced by the Gemmological Institute of America (GIA) in the 1960s.

Diamonds are graded on their colour but in actual fact it's their lack of colour which is most desirable. Colourless gems which appear 'white' are graded higher on the scale of diamond colour as they are more chemically pure, the most colourless being D with the gradual scale sliding all the way down to Z. Diamonds beyond Z colour are considered 'Fancy' diamonds and are scaled separately dependant on their intensity of colour.

Diamonds actually come in many colours with red diamonds being extremely rare and yellow being a more common fancy colour. Different elements within the stones atomical structure will influence its colour, along with changes made to the stone when under extreme conditions such as heat or pressure.

What is Diamond Colour?

For the most part, a diamonds colour will be graded on a scale from D to Z. This scale was first developed by the GIA (Gemmological Institute of America) in the 1960s. D is the top end of the scale and diamonds graded D are considered the most colourless and whitest on the scale, gradually the scale moves down to Z, these stones have an obvious yellow or brownish colour to them.

Before the GIAs introduction of the 4C's and especially when it comes to Old Cut Diamonds, the colour grading scale was not considered as important in determining value as it is today. Actually during the Victorian times, stones with a warmer hue were actually preferred, with slightly yellowish Old Cuts looking best with the low lighting and candlelight commonly used at the time. 

Grading Colour in Diamonds

When grading colour in diamonds the environment in which the colour grading is performed needs careful consideration. Outside factors such as wall colour or reflections from the surrounding environment can influence the colour of a diamond. It's important that the room is dark and there are no windows or daylight entering the room when grading. A special lamp is used to create a sole light source when grading, this means that the lighting influencing the colour of the stone is controlled and an LED daylight bulb is used.

Diamonds are colour graded from a side on position and usually placed in a holder made from white card so that a true colour grade can be achieved. Loose diamonds are placed table down into the holder and the colour grade is taken from the widest point of the stone where the most density of colour is shown.

D Colour Diamonds are considered colourless and the 'whitest' on the scale, subtle differences in colour appear as the scale progresses down to Z. Stones which are H Colour and above are considered 'white' and the differences between D-H Colour stones can be very difficult to spot to the untrained eye. However the colour grade can be a major factor in a diamonds quality, value and price.

What causes Diamond Colour?

Colour in diamonds can be caused by various factors, their atomic structure plays a big role in how they appear. Diamonds with more Nitrogen atoms spread throughout their Carbon structure appear more yellow in colour as the Nitrogen atoms absorb blue light and reflect yellow hues. Yellow or brown diamonds are the most common colour found in diamonds as Nitrogen is the most common atom found in diamonds other than Carbon.

Diamonds with almost pure Carbon atoms or very few Nitrogen atoms appear the whitest and brightest stones, as their structure is not interrupted in any way meaning no light is distorted when entering and exiting the stone.

Coloured Diamonds 

From red, to blue and green to pink, diamonds come in all colours. Coloured diamonds are graded differently to white diamonds, their intensity, hue and saturation are considered when grading. Coloured diamonds are given grades including faint, fancy light through to fancy intense and fancy vivid and deep.

Coloured diamonds get their colour from different factors, for example Pink Diamonds get their colour from Plastic Deformation, a type of extreme pressure   compressing and distorting the stones structure as it's forming in the earths crust, which then causes the reflection of light in the stone to be distorted.

Blue Diamonds are caused by Boron atoms being present in the structure and Green Diamonds are caused by irradiation! 

Fancy coloured diamonds are graded and described according to their hue, tone and saturation with deeper more intense colours making a stone more desirable and therefore valuable than those with paler colour.

Edwardian ring with yellow centre diamond recently sold

Enhancing or Changing Colour

Did you know that a diamonds colour can be improved or enhanced? High Pressure High Temperature (HPHT) treatments, irradiation and annealing can be used to alter a Diamonds appearance and those which appear slightly more yellow in colour can be treated to become more white, coloured diamonds can also be treated to intensify their colour. It's always best to check if a diamond has been in any way enhanced and this should be disclosed when purchasing.


Whether you like white Diamonds or those with colour, it all comes down to personal preference. There's no right or wrong! If you have any questions about diamonds colour then do get in touch, our diamond expert, Melissa Holt DGA, would be very happy to help.