When men and women really start looking into diamond grading, a common question is, “Why does the GIA color grade start with a D?”
GIA’s grading scale begins with the letter D, representing colorless, and continues, with increasing presence of color, to the letter Z. Diamonds are color-graded by comparing them to stones of known color under controlled lighting and precise viewing conditions.
Historically, metaphoric terms were used in the very old days. “River” and “water” were used for the most colorless diamonds, or they might be categorized by a geographic location from places where similarly colored diamonds were seen. For instance, there was “Cape” for pale yellow diamonds from the Cape of Good Hope.
The choice was made to differentiate the GIA grading system from other less clearly defined ones that used designations such as “A” or “AA”. Additionally, American Gem Society (AGS) had its own numerical scale, which was only for AGS member use. So when GIA chose to develop a diamond grading system, it had to use new terms. Hence, the “D.”