So that's why the girls I knew when I was a teenager spent so much time working on their tans and why women go to tanning booths and buy sunless tanning products. Or is it the other way around?
As I understand it this is a very recent phenomenon driven by the advent of colour film in Hollywood in the thirties (movie stars lived mostly in California - they developed tans - people want to be like their idols kind of a deal). This column in USA Today attributes the original fad to Coco Chanel in the twenties.
I haven't got time to dig any evidence up at the moment but I think you'll find that historically the ideal in Europe at least was for the skin to be as white as possible. This was certainly true in Elizabethan times in England where women used to apply a paste containing mercury to whiten their complection.
There is a preference for lighter skin tones in Asia and skin lightening products are big there but IMO these differences are primarily cultural.
And so is the preference for darker skin tones in Caucasians. I suspect both are recent developments.