What causes those mood rings to change colors?

Question

The dark rings that claim to be able to show you your "mood"

Answer 1

Body temperature determines the color of the ring :)

Answer 2

summer is right

Answer 3

I think by your body temperature. The ring itself contains  thermotropic liquid crystals.The crystals respond to changes in temperature from your body. Personally, I believe it does work, sometimes.

You can Google "How Do Mood Rings Work?

By Anne Marie Helmenstine" for more information.

Answer 4

"Liquid Crystal" is the key ingredient in all "Mood Rings" & other types of "Mood Jewelry" that does the color-changing.  The molecules of the "Liquid Crystal" respond to your surface body-temperature (& somewhat the surrounding temperature as well)- Then begin to move/shift in response to the temperature changes, thereby reflecting & refracting light differently, thus causing the color changes.