When does it stop being referred to as racial differences and instead referred to as cultural differences(regardless of which racial sub-culture the current culture was borne out of)?
When America catches up with the rest of the developed world and stops lumping individuals with complex multifaceted genetic backgrounds and mixtures into ridiculous, segregated, monolithic groups?
To clarify, "racial differences" generally meant "genetic differences". So a better way to put it is not race vs. culture, but genetics vs. culture, as ethnic groups (or more broadly speaking, races) can have both different genetics and different cultures. In other words, nature vs. nurture. You take people of different races, look at the differences between them and then study how much of the variations are due to genetic or environmental causes. "Racial differences" I guess could mean both genetics+culture.