Just like if you were to purchase a $10-$20 value costume ring from your local department store, because of the materials that are used in rings they may turn some people’s fingers green. Some people find some rings have this effect while other people don't have any problems at all. Most agree that it comes down to individual body chemistry.
Not to worry, a simple trick to stop the green coloring is to coat the inside of your ring with clear nail polish. You should find you don't have the problem anymore with your Diamond Candles $10 level ring or any other costume jewelry that you own.