Some mood ring colors and they meanings are; black which is associated with negativity, red is associated with passion and anger, yellow is associated with mental processes and green is associated with growth. We also have blue which is associated with relaxed mood and white is associated with frustrations.
Oddly, mood rings contain crystalized cholesterol, which changes color according to slight variations in temperature. Don't know about liquid cholesterol, but who would wear that? Messy! Anyway, your skin temperature varies slightly with your emotions, and that effects the color of the crystalized cholesterol. Don't know what each color means though. I've read descriptions of what they mean which were almost opposite to each other. But that is WHY mood rings, etc, change color. Temperature.