The diamond colour scale developed by the Gemological Institute of America (GIA) starts with the letter « D ». A completely white diamond will therefore be classified as « D » and not « A ». This choice was made by the GIA to differentiate its grading system from other, less precise systems that use classifications like « A » or « AA ». Furthermore, the American Gem Society (AGS) has its own numerical scale, which was restricted to AGS members only. So, when the GIA decided to develop its own diamond grading system in 1953, it had to introduce new terms. Hence the « D ».