Heat absorption and reflection has almost nothing at all to do with skin color. Black things do tend to absorb heat well (although black holes are a completely different thing and have nothing at all to do with this), but more importantly for human skin, melanin absorbs UV light before it can penetrate and damage DNA. You need lots of melanin in areas where there's lots of sunlight, or else you'd have lots of cancer.
Different wavelengths of light absorbing different amounts of heat is of course a real phenomenon. But your reading into the lamp experiment and melanin deposition is a little muddled. It would appear that the black cover was absorbing, and therefore carrying (at least some of) the heat away from the lamp. Whilst the white one was reflecting at least some of it, making it warmer. Given this, and the fact that black absorbs the most heat, those with darker skin pigments would actually be absorbing more heat. This is obviously not a preferable trait in a hot climate. But the reason for heavier melanin deposition benefits more than this drawback. This is the latter suggestion you made - UV light protection. Melanocytes (cells containing melanin) absorb the UV light energy and dissipate it away relatively harmlessly, giving protection from direct sunlight. This is why there is a strong correlation between melanin deposition and latitude. As you move north and south away from the equator, the human populations become progressively lighter in skin tone. Look at this representation for that point https://www.google.co.uk/search?site=img...
Your last point about black absorbing light 'like black holes' is coincidental, the reasoning is very different !
