1
It was not India but Europe which first invented the word “Casta” linking purity of blood & skin color to status in society. Hindus never had a word that meant caste. It's a racist term connoting white superiority as the measure of intelligence, civilization and morality.
2
"Casta" is an Iberian word meaning lineage. It is documented in Spanish since 1417. It is the root of the English word caste. It was historically used as a racial and social identifier where colonial Spanish & Portugese societies had a hierarchical race-based "caste system".
3
Originating from the Spanish concept of purity of blood called "Limpieza de sangre", during Christian conflict with Islam, Casta was used in Christian Spain to demarcate those of Jewish or Muslim heritage who were usually convicted by the Spanish inquisition for heresy.
4
Only the “Old Christians” who had “Limpieza de sangre” or purity of blood, had high social status. So it was Christian religious extremism during the Inquisition with its ideas of racial superiority and purity of blood that created the original Sistema de Casta or Caste System.
5
In the 1500s, the Spanish solidified the ideas of purity of blood & Casta as directly associated to skin color and percentage of “white blood” in a person. Anyone with a lineage even inked to a dark skinned ancestor was tainted by a "stain" due to that connection.