From Antiquity to the XVIIIth Century, India was the only producer of diamonds.
Two wonderful manuscripts (considered to be lapidaries) dating from the VIth Century summarize the elements that at the time were considered essential for the value of a diamond: purity, clarity, color, brilliance, fire, hardness and above all, rareness.
The color of a diamond was at the time closely associated with the caste system. The priests (Brahmins) alone were allowed to own white diamonds. Warriors and knights (the Kshatriyas) could have red diamonds (probably not real diamonds, but spinels). Yellow diamonds were attributed to the Vaishyas, i.e. the landowners and merchants. Finally the artisans and peasants - the Shudras - could acquire gray and black diamonds, if they had the means.
Little information exists concerning the birth of the commercial diamond routes, but manuscripts dating from before the VIth Century refer to diamond exports to the West originating from the plains of the Ganges.