Genetic change, caused by continuous variation with phenotype(environmental factors)???Hypothetical question?

So continuous variation occurs due to environmental factors, which lead to mutation that lead to change in phenotype and hence genotype. If we put a person and his next lets say 50 generations under the sun under constant sunlight, the 50th generation will all have black skin, as this is how africans have their black skin rite? So what if hypothetically we reverse the change, lets say we put a black man in dark environment with no sunlight whatsoever( since its hypothetical dont bother about food, warmth etc etc). So would his next 50 generations turn white?? If so then if we put a black man in the antarctic will his 50th generation be white? p.s- I am just using black to make it simpler, no racism or anything..:)