D COLOUR
‘Diamond colour is all about what you cannot see. Diamonds are valued by how closely they approach colourlessness – the less colour, the higher their value. The exception to this is fancy colour diamonds, such as pinks and blues, which lie outside this colour range. GIA’s colour-grading scale for diamonds is the industry standard. The scale begins with the letter D, representing colourless, and continues with increasing presence of colour’
Gemological Institute of America