You could group people by hair color or eye color as well, without reference to any society. But, the social importance of that grouping could vary greatly bet

You could group people by hair color or eye color as well, without reference to any society. But, the social importance of that grouping could vary greatly between societies. Eg. not many people care about who is an Ionian or an Achaean in modern society. The racial distinctions (at least today in the west) are associated with biological traits, and specifically the ones that are visually obvious. But, I think those biological traits are used socially to distinguish groups that are considered different for other reasons (values, beliefs, etc.).