I agree, that could be the case. If they raised a black kid around black women his whole life, and then around the age of 20 he was put around white women. Would he find white women more beautiful? If he does you could make the case it’s only because they’re new and ‘exotic’. So you do the same with someone initially around white women, then when he’s 20 you make him meet black women, what would they say?We don't know if preferences are a product of nurture and/or nature. It's likely both.
We also don't know if those guys in Mauritania have a genetic predisposition to prefer thicker women.
Something I noticed is people of African tend prefer big butts regardless of how they raised up compared to guys of European descent who prefer them flatter.
That would be the only way to prove if it’s in our nature to prefer lighter skin, and those features.