This is not true. Even ancient Chinese had a strong preference for light skin tone. My understanding is that darker skin usually means a person is more exposed to sunlight, presumably from farming work, which is an indicator of lower social status.
>>This is not true
You can't really claim that America's history & media has nothing to do it. You can debate to what degree, but to dismiss it completely is impossible.
If the preference were an idealized optimal algorithm, perhaps; but people are adaptation-executers. The simplest rule is 'lighter skin means richer', and so when one runs into an African, it's not necessarily perfect. (Although given how many poor African immigrants there are in China now, I'm not sure that's a bug rather than a feature.)