The oxidation of different chemical components can create flames of various colors. Trace amounts of copper and copper alloys found within a fuel source are able to produce a distinctive green flame when they are burned.
According to the University of Wisconsin, when heated to the proper temperature, molecules release energy within the spectrum of visible light. Old newspapers and other common materials that contain trace elements of copper compounds create a green flame when they are used to fuel a fire. This is the same effect that is often used in the creation of fireworks to make more colorful explosions.