This is due to the relation between temperature and the wavelength of the radiation emitted by copper. They are related by Wien's law, and they are inversely proportionally to each other. read more
its because of the oxidation process that copper undergoes which makes the copper to take different colors while heating. read more
Copper(I) oxide (cuprous oxide, Cu2O) , red color forms below 300 C Copper(II) oxide (cupric oxide, CuO), brown,black oxide that forms above 300 C Continued heating to 1326 C results in melting and at 2000C, it boils. read more
Copper carbonate the solid doesn't have the same water there and this is usually a greenish colour. Incidentally the copper sulphate, the crystals itself are blue but that's because they also have water trapped in their crystals. If you heat them up and drive out the water they actually go white and colourless. read more