Depending on the time a torch has been on the copper it will go from a gold color, then orange, pink, purple, dark blue, and light blue. But why does it do this?
That's actually a very interesting, thoughtful question. I'm a pro jeweler and I'm a chemistry buff but not a professor or anything. It's very simple and also very complicated at the same time. Copper oxidizes quite easily in the air. There are two things in the air that it oxidizes with - oxygen and sulfur. Oxygen is there naturally, sulfur mostly comes from industry and cars, though you usually can't tell with your nose. So, when you heat the copper it is forming oxides and sulfides, which are different colors, and the more you heat it the more oxides are formed. With copper there is another factor - copper has two valences so it forms cupric and cuprous oxides and sulfides, meaning there are actually four compounds being formed under heat. Your orange, pink and purple are actually deeper shades/layers of one oxide, the blue and blacks and greys are varying layers of another, etc. You can look up copper in Wikipedia or a book and get more fundamental info about it, but that's generally the answer to your question.
