The colors and general meanings of mood rings and necklaces are: violet (happy, love, passion), blue (relaxed, calm), blue-green (somewhat relaxed), green (average), amber (mixed emotions, nervous), gray (anxious) and black (tense, nervous). Mood jewelry was popular during the 1970s.
Mood jewelry was created by Joshua Reynolds. The stone of mood jewelry is made of a hollow glass or quartz shell which contains liquid crystals that change color based on the heat of your skin. When the temperature changes, the molecular structure of the liquid changes, which then changes the wavelengths of light. This results in a change of color. At normal body temperature, the mood stone is green. As temperature increases in response to happiness, the stone color moves towards blue and violet. When a person is upset or anxious, their skin temperature decreases as blood moves toward other organs. This changes the color to yellow.