People often wonder why the color grading scale starts at D and not at A. The answer to this is actually a very simple one. At one time, the colour scale actually did start at A. In addition to starting at A, colour systems were also assigned numbers (0, 1, 2,3), Roman Numerals (I, II, III) and even (AA) . Classifications such as "gem blue". "fine white". "blue white". Were used as colour descriptions. These colour grading systems were loosely applied and often times, inaccurate and inconsistent. Early on, when the diamond trade developed, diamond grades were developed by various parties within the trade. These original scales never included the letter D and when the Gemological Institute of America (GIA) created the new scale in 1953, they decided to start fresh with a letter that wasn't a part of the previous grading system.
The GIA scale is now the official colour grading scale and has universal acceptance among laboratories and trades-people. This current scale ranges from D to Z, with D being colourless to Z which is a light yellow or brown. The term colour in regards to diamonds actually increases to its lack of colour and the less colour a has, the rarer and more valuable it's. Brown or yellow diamonds that have more intense colour than Z on the grading scale are considered "fancy colours". These diamonds are graduated by a separate system entirely and this same system is typically used for grading coloured gemstones like rubies, sapphires. Emeralds.