Why do elites have blue blood?

The notion of "blue blood" among elites is a historical concept originating in Spain during the 16th century. It referred to the perceived paler skin tone and visible bluish veins of the aristocratic class, which they believed was a sign of purity of lineage. This association arose due to the belief that the old Castilian nobility had not mixed their blood with that of Moors or Jews during the Moorish rule of Spain, and therefore possessed "purer" blood.

However, this idea is not based on any scientific evidence and is merely a social construct. Blood color is determined by the amount of oxygen it carries, not by social status or lineage. Elites do not literally have blue blood; the phrase is used figuratively to denote their privileged social status and perceived superiority.