I had one, long gone now though...the color of the stone would change, supposedly according to the persons mood! Of course we know the color change is due to the wearers body temperature fluctuation but then our body temperature does change with our moods...besides the idea of the color changing with our mood was more fun!!
In the fall I came across a new generation of "mood beads", purchased a few strands and made necklace, a couple of bracelets and rings, customers loved them. The necklace was particularly interesting because when the customer tried it on we saw a whole range of colors, as the beads don't all touch the body to the same degree. After all this time people still enjoy the idea of the beads changing color on their body...they are fun!! I've just made a few more bracelets and though I would share a few photos of the color changes.
This bracelet shows colors ranging from dark to medium brown to a tiny bit of yellow and green in the bead front left...

This is the same bracelet after I held in in the palm of my had for 10 seconds or so...you can see a nice rich cobalt blue...although the one bead front/left is showing a slight bit of green...
The man behind the idea of Mood Rings is Marvin Wernick, who in the 60's happened to watch a doctor friend use a heat sensitive liquid crystal plastic strip which was developed to take children's temperatures easily. At the time Marvin was a jewelry maker and saw great possibilities for this product. He made rings using a this product but unfortunately he didn't patent the idea and another fellow used the idea and made millions!
Look at all the colors here...dark green, teal, brown, a rusty shade...
This is a different bracelet but again we have dark/medium brown, dark/medium green, rusty brown...
Hope you enjoyed the walk down memory lane...
Cheers