Grading colour in the normal range involves deciding how closely a stone’s bodycolour approaches colourlessness. Most diamonds have at least a trace of yellow or brown in their bodycolour. With the exception of some natural fancy colours, such as blue, pink, purple or red, the colourless grade is the most valuable. The GIA Diamond Grading System uses letters to represent colours, beginning with D (colourless) and ending at Z (light yellow or brown).