There are three important factors to understanding the colour of pink diamonds: hue, tone and saturation.
Hue is the dominant colour of the diamond; tone is the amount of light or darkness in the diamond; and saturation is the strength of hue. The more intense the colour, the rarer and more valuable the diamond.
For fancy coloured diamonds, the 'C' for colour typically outweighs the other three 'Cs' of clarity, cut and carat weight when it comes to grading and value, particularly in the case of Argyle pink diamonds, whose value increases along with the intensity of colour.
The presence of colour in pink diamonds remains a mystery, but it is certain that it is not derived from a predominant trace element or impurity. In the case of Argyle pink diamonds, it is thought that extraordinary pressure more than 160 kilometres below ground raised the diamonds to the surface and it has been established that the twist in the crystal lattice is present in all pink diamonds, refracting light and producing colour. Levels of nitrogen appear to also be important, with lower levels favouring pink colours.
"SLOW BUDS THE PINK DAWN LIKE A ROSE FROM OUT NIGHT'S GRAY AND CLOUDY SHEAF; SOFTLY AND STILL IT GROWS AND GROWS, PETAL BY PETAL, LEAF BY LEAF"
Susan Coolidge, from the poem The Morning Comes Before The Sun
Fancy red is the most coveted colour and only a handful ever see the light of day. Less than 3% of all tender diamonds have received a Red GIA classification.
While clarity and carat weight ordinarily impact on the value of white diamonds, these characteristics are less of a consideration in the value determination of Argyle pink diamonds, with the focus instead being on colour and cut.