I imagine there is a particular chromosome were its gene specializes in producing melatonin, were the color of the skin surface will be permanent or there can be an epigenetic process were some methylation blocks the melatonin gene from expressing itself and the color of the skin will be lighter in color . As consequence we will have a color of skin surface reversible.due to environment
You seem to be talking about melanin, not melatonin. Humans respond to UV exposure by boosting melanin production in their skin cells - outside of genetic defects such as albinism, essentially all humans do this to some degree. It's more noticeable individuals with less melanin in their skin to begin with. So skin color in humans is "reversible" due to environment, to some degree. Why do you ask?
