What is Verdigris? It is the green pigment caused by acids on metal.
After a frame is soldered it is dipped in a mild acid solution followed by an acid neutralizing solution to clean the joint. If any acid is trapped in a crevice vedigris may result. Many metal frames of various eras have this problem and it can be seen on purse frames near solder joints. It is especially common on the soldered grid design frames of the 1940's which also had copper and brass beading wire.
In my former life as a metalsmith, verdigris was often encouraged because it was such a beautiful turquoise color. Check out your local paint store or craft supply, and you will find patina kits to create this look today. Unfortunately for these beautiful frames it was a undesirable coloration.
The application of vinegar or ketchup can reduce the discoloration, and a baking soda in water solution can neutralize any remaining acid. Make sure you rise the frame to remove any residue.
Frames can be recolored using a guilders paste.