In 1953, the Gemological Institute of America introduced what is now the industry standard grading scale for colorless diamonds, grading them on a color scale from D to Z and a clarity scale from Flawless to I3. At the time the new grading system was introduced, several grading classifications were used that employed numbers, letters and descriptive words. This caused confusion when comparing two diamonds that had been graded with different nomenclatures. D was agreed upon as a starting point to differentiate from the previous systems.
