If you remember the 1970s, you probably remember the ever-popular mood ring. The mood ring shot to fame in the 70s, and virtually everywhere you turned you could find someone, somewhere sporting a mood ring. A mood ring has a special stone on it that is supposed to turn a different color based on the mood of the person wearing it.
Technically, the mood ring doesn't really change color due to your mood. A mood ring changes color based on body temperature. If you are happy, you tend to flush or get warm. The ring turns color based on your body warmth. If something is bothering you, your blood often begins flowing away from your fingers toward your organs, thus causing your fingers to be less warm. The stone turns a different color as a reaction to the coldness in your fingers.