From The Conversation:
by Daniel Zizumbo-Colunga
Some of this is genetic, while some is likely due to indoor/outdoor labor class differences: i.e., people with a lot of education get office jobs while people with little education get outdoor jobs and tans.
In Latin America, skin tone genes often don’t correlate as much with other genes as in North America.
Because there is more of a color continuum than a color line, there is more of a premium in Latin America put on genes specifically for fairness: for instance, the fairer sister is likely to marry up the social ladder and the darker sister down.
Rinse and repeat this kind of selection over many generations and you can get a lot of disjunction between looks and ancestry. Mexicans made a whole lot of movies in the 1950s about fair upscale couples who have a dark “throwback” babies. In general, in Mexican movies, African looks were seen as more socially scandalous than Amerindian looks.