Why is it green?
No, nothing to do with copper - that's school chemistry lessons where you put copper powder in a bunsen burner and the flame goes green.
For bolides, it's to do with atomic excitation of the atmosphere and the frequency that different species reradiate at. If Gary was still here he could add some details about this, but most of the light you see is due to hot atmosphere, not hot meteorite or even to metoritic contamination of the atmosphere.