The phrase "one's winter skin" is an idiomatic expression that refers to a person's physical appearance, particularly their complexion or skin tone. It suggests that one's skin may appear different during the winter season due to various factors such as exposure to cold weather, dry air, and indoor heating which can cause the skin to become drier, flakier, and sometimes paler in color. The phrase is often used metaphorically to describe a person's emotional state or behavior during the winter season, suggesting that they may be feeling withdrawn, less social, or more introspective due to the cold weather, shorter days, and longer nights.