This popular fad became famous in 1975 when it was invented by New York inventors Josh Reynolds and Maris Ambats. These mood rings are sold for the purpose and promise of being able to change color to the color of the mood the wearer is in. For example, if the wearer's ring were to turn black, the color code says that the wearer is supposedly stressed. There are hundreds of color codes for these mood rings. In actuality, the ring is a "specialized liquid crystal thermometer". Changes in body temperature is detected by the thermometer, thus causing a change in color in the stone. Therefore, the ring has nothing to do with guessing your mood. Body temperature and moods have no relation with each other. The fad is still popular today, mainly with young children.