Bronze contains copper, and when copper comes into contact with the oils and acids in your skin, it can cause a chemical reaction that produces copper salts. These copper salts can turn your skin green, which is a harmless reaction and will go away on its own. The extent to which brass will turn your skin green depends on factors such as the amount of time you wear the brass jewelry, moisture levels, and the pH level of your skin. It's worth noting that not everyone's skin reacts to bronze in the same way, and some people may not experience any discoloration at all.
There are a few things you can do to mitigate: make sure to keep it as dry as possible and take it off while you're sleeping. Some people choose to put a thin layer of clear nail polish on the inside to create a barrier between the metal and your skin.
We choose not to gold plate any of our jewelry, especially rings, because the plating will always rub off and eventually you will have the same reaction to the metal underneath. We use solid bronze because the color of the metal will not rub off and it can always be repolished.
If the green cast bothers you we recommend sticking to silver or solid gold.