FREE: Uni-Sex, 3mm, Silver-tone, Plain, Rounded, Ring/ Band - Size 10

When a ring turns your finger green it's either because of a chemical reaction between acids in your skin and the metal of the ring or a reaction between another substance on your hand, such as a lotion, and the metal of the ring.
There are several metals that oxidize or react with your skin to produce a discoloration. You can get a noticeable green ring around your finger from wearing a ring made using copper. Some rings are pure copper, while others have a plating of another metal over copper or the copper may be part of the alloy (e.g., Sterling silver). The common green color is not harmful of itself, though some people experience an itchy rash or other sensitivity reaction to the metal and may wish to avoid exposure to the metal. This is a silver alloy with no copper so it will not turn his finger green.