The mood ring (that one can wear)  is a specialized liquid crystal thermometer first sold in  August, 1975, and was a huge success.

The ring is usually made of quartz or glass which is either a clear capsule filled and  has a thin sheet of liquid crystal sealed underneath. Changes in temperature cause the crystal to reflect different wavelengths of light which changes the color of the stone. The liquid crystal used in mood rings is usually set up to display a “neutral” color at the average human skin temperature, which is approximately 34 °C (93 °F)

Many companies at that time sold 30,000 to 40,000 a month for a while. This got in on the craze and then, like many fads, it was over.They initially retailed for $45 for a “silvery setting” and $250 for gold.

The Bizarre Bazaar, that cavernous Wells Street emporium that has been there since 1960 and retains the feel of what used to be called a “head shop,“ was open and, sure enough, carried a large selection of the rings, along with mood bracelets and mood amulets, hanging from golden chains.

The amulet had come with a guide to the ring`s different colors and their meaning:

If it is brown-black the wearer is tense, if green content, if blue very happy . . . and so on.

Chicago Tribune.