The thermotropic liquid crystals in a mood ring twist and change colors when the peripheral temperature of the wearer changes. If the outside air is very cold or the stone is damaged, the color of the stone turns black.
When the skin of a person is at normal temperature and the person is calm and relaxed, the stone is blue. If the person starts to feel happy or romantic, the blood rushes toward the skin, which raises the temperature, and the stone turns violet.
The stone turns green if the wearer is in a resting state. When the wearer feels excited or nervous, the blood moves away from the skin to the internal organs, and the skin cools, turning the stone yellow, brown or gray.