Most gem quality used in jewellery are colourless and nearly colourless, sometimes with tints of yellow and brown. Among the rarest are the colours D, E and F on a scale that goes to Z.
Colour grades are established by comparing each diamond to a set of each master comparison diamonds. Each grade represents a range of colour. Grading colour is done in a specific and controlled lighting environment and according to strict colour grading procedures.
More colour intensity than Z is called "fancy" colour. Diamonds of colours can be found in nature; over 300 colours have so far been identified, however these came in an infinite numbers of shades and hues.