Most people are alarmed when the find their jewelry tarnished or their skin discoloring from wearing their jewelry. I have heard it more than a thousand times when customers try to buy a piece of jewelry "Is This Ring Going To Turn My Finger Green ? ". The first thought that crosses their minds is that they got ripped off and the jeweler sold them something fake. Here is an article that explains what causes your gold or jewelry to change colors or discolor ones skin.
http://www.thehypnotique.com/kb_results.asp?Cat=39
