This might sound funny, but I have a mood ring and after I wear it for a couple of days, there seems to be a greenish-dark bluish color of skin where my ring was. I take off my ring when I sleep, and when I wash my hands, my ring always comes off. What is this and why does it happen?

some metals oxide or react to chemicals in your skin... think wearing copper turns you green...

Not at all uncommon for some metals. I paint my rings that do this with clear polish. It needs cleaned off occassionally when it yellows. There are cleaning solvents on the market made for jewelry.

costume jewelry will often turn your skin colors. Real gold and sterling silver won't.