What if all humans developed the same skin color?

[Paul Spring]

Inspired by discussion in the "One-continent humanity" thread over in the ASB forum ....

The exact reason for why different groups of people have different skin color/shading has long been disputed. The most plausible answer is that it is an evolutionary adaptation to different levels of sunlight. The more sunlight an area gets, the more melanin or skin pigment the people living there need to shield themselves from ultraviolet radiation. People living in low-sunlight areas, generally at higher latitudes, need much less pigment - in fact, having too much of it could block out too much ultraviolet light.

Yet, there are certain exceptions to this rule. The many different groups of Australian aborigines all have dark brown skin, even those who lived in the southernmost parts of the continent, and on Tasmania - areas that are relatively temperate and have less intense sunlight than hotter regions further north. Within certain zones of latitude, there is still a considerable variation of skin pigmentation. Some groups in Africa, such the so-called "Bushmen" in the Kalahari desert, have skin that is considerably lighter in tone than others. People who lived in subarctic areas of northern Europe had very pale skin, but people who lived at similar latitudes in northern Asia and North America had skin that was darker by comparison.

What if at some point during the evolution of modern Homo Sapiens, genes that caused wide fluctuations in skin tone never develop? Suppose that regional differences in bone structure, hair, etc still happen as in OTL, but virtually every human being on earth has skin that is medium-dark brown in color. How might this effect human society, culture, and history?