Skin color is related to their natural DNA. A person's DNA will never change unless it is modified with some extremely advanced technologies. So generally speaking, DNA will not change, that is, its sequence will not change, and the skin color it controls will not change much. Because DNA controls human skin color, people born with dark skin will not become very white because of seasonal changes, and people born with white skin will not become very black because of changes in the external climate.
Generally speaking, people turn black for two reasons. On the one hand, it is controlled by DNA. On the other hand, ultraviolet rays from the sun irradiate the human body and then produce melanin, so that the skin color will turn black. People's common skin color turns white in winter because it is cold outside and the sunlight is not strong in winter. People expect to stay at home for a long time and reduce their exposure to ultraviolet rays. Melanin is gradually metabolized and reduced, and then the skin will turn white.
Compared with winter, people's skin color will be obviously different. After all, the sun is strong and the ultraviolet rays are strong in summer. At that time, people also liked to do outdoor sports, such as climbing mountains, fishing and playing football outdoors. When the human body is exposed to ultraviolet rays in a large area, the melanin in the body naturally increases and the skin color turns black. Winter is colder than summer, and there is no strong sunshine. Outdoor sports are reduced and the skin is covered with thick clothes. Even if you go out, the skin area exposed to ultraviolet rays is not much, and the melanin production is significantly reduced. It is normal for the skin to turn white after metabolism.
But the degree of blackening and whitening is limited. For the yellow race, generally speaking, even if you exercise in the hot sun for a long time in summer, your skin color will not turn black, and even if you don't go out in winter, your skin color will not become extremely white.