Why do dark-skinned people stay dark after migrating to low-sun regions, and does skin color have its own DNA code?

It is not easy, and I do not pretend to be the expert on this; I just use logic. Once people got into a certain place after the flood, I think it is obvious that our DNA structure is built for adaptation, and that is the marvel of DNA: it can vary depending on the environment. This is adaptation, not evolution, because adaptation is the same species adapting to a different environment, whereas evolution claims one species develops into a higher species by time and chance, which is yet to be proven. Noah and his family carried a very large gene pool from Adam and Eve, and that pool only gets bigger down the generations, so you can carry a gene from a great-grandfather that your father does not seem to have. So people near the equator get more solar exposure, and the DNA reacts by producing more melanin, which is in one of the lower of the skin's seven layers and comes to the surface with more sunlight to protect against ultraviolet light and cancer. People in the north, in Sweden, Finland, Russia, Canada, get much less sun, so their skin does not need as much melanin and stays light. How every detail works out I cannot say, and the theories out there are all tainted by evolution, but the general answer is our God-given DNA structure adapting to the environment, along with the flood and its aftermath dispersing people and animals across the separating continental masses.