Certain people believe that your ring turns your finger green because it's not real silver. However, this is actually not the case at all. The ring turns your finger green because of a chemical reaction with your skin's moisture and the alloys in the metal. This moisture can be as simple as water, sweat or humidity. For silver rings especially, acids commonly found in the air, water, lotions, soaps produce a reaction and cause it to tarnish or leave a dark green ring on your finger.
Certain people find that some rings have this effect, while people never have problems at all. At the end of the day, it also comes down to body chemistry. Similar to high end costume jewelry, materials that are used may turn your finger green.
Now that you are aware of the causes, we encourage you to take measures to take care of your ring and prevent it from tarnishing or turning your finger green.
Any precious metals will require special care. White gold will need rhodium plating every five or six months. Certain metals like stainless steel will not tarnish. You can apply a thin coating of clear nail polish so it will not tarnish or turn your finger green.