Why does blue represent sadness?

Represents a melancholy soul, which can also be understood as yearning for freedom and the color of blue sky. Then it is as wide as the sea. Blue can represent the ocean, that is, it has an infinitely broad mind of the ocean, as melancholy as autumn water and as unpredictable and mysterious as the ocean! Foreign representatives are calm and wise. I like blue, I think it is mysterious and noble. Blue is the most beautiful and noble personality in the soul.