When grading the colour of a diamond, the grader is actually measuring the absence of colour on a scale from D-Z. The grade is established in controlled viewing conditions and in comparison to master stones, with D referring to a colourless, exceptional white diamond, and Z being ‘fancy’ yellow or tinted.
This scale is only used to grade ‘white’ diamonds, while fancy or coloured diamonds use a different system that grades them on the intensity of their colours, as opposed to the lack of. Generally, if a diamond presents more yellow or brown tones than a Z master stone, it will be classified as fancy.
Using this scale, the whiter and less colour a diamond presents the higher the value and price. While D is considered the most valuable, the difference in colour to the naked, untrained eye between a D and a G grade diamond is almost invisible. This is important to remember when choosing your perfect diamond, as it may be more achievable than you think.