Do you happen to have the title of Mr Smith's book handy. Sir?I think If you check Ron Smith's book You may find that he didn't use copper but different alloys of gold silver and copper to get the desired look. It is amazing what he has done to get the different color inlays. I'm sure that copper would be OK for case coloring. But, I'm no expert on this. I do know that dissimilar metals, when in contact with each other can cause problems and it might cause the inlay to decay and come out. Using gold alloys such as white gold and pink gold would solve the problem as the gold doesn't react with other metals so well..