Cleaning

It's just oxidation. Your frames are made of brass or a brass alloy and brass exposed to air oxidizes. They probably had some kind of coating on them when they were new.

Get them clean and then, very carefully, coat the metal with clear fingernail polish. That should keep them from turning green to match your eyes.

Joe(Here's looking at you, kid)Nation

Thank you for the information, Joe Nation. It so happens that I bumped into a door the other day and broke my nosepads. I went to an optometrist and have decided to get titanium frames. I needed new lenses anyway.