The problem which comes from attempting reverse evolution is that evolution did not happen in leaps. It happens in micro events. Some as minute as a change in the structure of a protein, while this may seem like nothing studies show (such as the recent studies on AIDS) that it can benefit the organism. Over millions of years those changes build up and you get a change in the original organism that may be enough to call it a new species. Humans, like all other living organisms are subject to change and adaptations. The melanin in our skin which gives it a dark color has been subject to those adaptations. In cooler climates some melanin genes have stopped functioning. That is because the dark pigment of the skin needed in places like Africa are not necessary in cooler and darker climates. One function of the melanin is to prevent damage to the DNA. The more sun hitting the skin, the more the pigmentation has to work. While this helps prevent mutation and destruction of the DNA it also hinders production of vitamin D when the skin is too dark in dim lit places. So in colder and darker areas the amount of pigment would not be necessary. This is probably what triggered the mutation for genes that do not function to produce melanin as much to occur, and since it benefited the offspring and they survived, it continued.
In climates where the skin is exposed to higher levels of UV radiation the genes for melanin are vital. People who suffer from albinoism often suffer retinal damage as well. It is not beneficial and they can’t adapt to their surroundings if they live in bright lit areas with much UV exposure they face great risk of cancer based on DNA damage.
So those in higher altitudes, and in hot dry areas would need to produce the largest amount of melanin, to protect the skin from intense amounts of UV radiation. While those in lower and wetter climates would need less melanin so they could produce the vitamin D thier bodies need.
When it comes to reversing all of this processes it would be hard. In people with lighter skin the genes which produce melanin are actually mutated and no longer function. While some of them do. The dark/light ratio of skin shows the amount of mutated genes. Eyes that are light blue with very pale skin show that most of the genes for melanin are not functioning. This trait is inherited from parents, but likely both parents carry the mutation. If only one parent carried the mutation then when the genes are shuffled and the offspring is produced the functional genes would likely be used verses the mutated ones. The original eye color, and skin would have been dark to black for all humans. It was the movement of our species into other environments and adapting that changed the need and function of these genes.
The change in environments has also caused micro changes in humans as far as facial structure, height, and body. The reason for these changes is environmental as well. While race may be a social construct it does exist in micro amounts on the DNA. That is because it has shaped who we are. People in dry sandy areas tend to have a sloped nose so that sand and dirt do not easily enter the passageway. While people in areas where nutrition is poor tend to be short. Each region has seen adaptations. This does not define race. Because genetically the variance is not significant, given millions of years it could become a variation in our species, but humans have too much social and mating interaction. This does explain the diversity we see, and why we say all groups look similar. People in similar regions have to adapt the same way, and breeding within a common gene pool means selecting from well adapted mates, as time goes on the survivors who are best adapted pass on the most genes, and those shape the gene pool we see today. It also explains the diversity in the African gene pool. Since mating practices in Africa were about dominance and diverse mating. In Africa due to the eco system many people have had to shift living areas, as well as have shifted mates, and that gave opportunity to diversity. While in other areas the isolation of populations and survival rates of offspring and breeding habits has led to a less diverse amount of genes. So while there is diversity, it is not as intense as those in Africa where man originated.