According to the situation you described, a 40-year-old woman may have some uneven skin color problems, such as yellow face. In this case, the blue vest is a good choice. Blue is a bright and refreshing color, which can bring a bright feeling to the skin and make the yellowish skin look healthier. This kind of cotton vest can provide a comfortable wearing experience, because cotton fabric is breathable and soft, suitable for long-term wear. In short, for a 40-year-old woman, wearing a blue cotton vest is a good choice, which can add bright colors and a sense of relaxation.