Being dark has, for perhaps thousands of years, been considered disadvantageous in many cultures...but not all of them.

I think that one of the main reasons for that was the simplest one: rich people tended not to have to work outdoors a lot in the agrarian ages that preceded the industrial revolution, while poor people generally spent their lives working outdoors. Thus rich people tended to stay pale and poor people tended to tan darkly.

Almost everyone would rather look upper class if they can...hence the prevalence of prejudice in favor of lighter skin tones. This was true in Europe, throughout Asia, and in some African cultures too. I'm not sure if it was a factor in the Americas, prior to the arrival of the Whites, but it may have been in some places with more of a "city" culture, as in the case of Aztecs, Mayas, and Incas.

Now, since the industrial revolution occurred, things have changed! Rich people are now MORE likely to get a tan (and to want one) than poorer people, because the poorer people have mostly gone to indoor work and they don't have as much leisure time to get out in the sun.

Thus having a tan is now fashionable. It looks "rich". John Kennedy, for example, looked "rich". Nixon didn't! Nixon was pale, but Kennedy looked like a "bronze god", according to people at the time. Kennedy's healthy and charismatic appearance was the biggest factor in getting him elected over Richard Nixon.

Ironical, isn't it? People are really pretty predictable when it comes to that sort of thing. They always want whatever is rarer and harder to get, whether it be a lighter skin tone or a darker one.

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I chose not to address racial issues in this post...only skin tone issues. The racial issues are many and complex, and they can change radically as time goes by. Whichever race is "on top" in terms of political and financial power...and that can change...that race is the one that ends up thinking of itself as superior at any given time. Such thinking is illusory, of course, but it's very persuasive in influencing people's view of themselves and others.