A mood ring contains liquid crystals that change color in response to small changed in temperature. The amount of blood that reaches your skin depends on both the temperature and your mood, so there is some scientific basis for the functioning of a mood ring. For example, if you are under stress your body direct blood toward your internal organs, with less blood reaching your fingers. The cooler temperature of your fingers will register on the mood ring as a gray or amber color. When you are excited, more blood flows to the extremities, increasing the temperature of your finger. This drives the color of the mood ring toward the blue or violet end of its color range.
Amber: Nervous, unhappy, cool
Green: Average, calm
Blue: Emotions are charged, active, relaxed
Violet: Passionate, excited, very happy
Black: Tense, nervous (or broken crystal)
Gray: Strained, anxious
The color of the warmest temperature is violet or purple. The color of the coolest temperature is black or gray.