When heating steel you may notice changes in color on the material (such as in a picture during the bending of this table leg). The Scale Model EXchange have an interesting color spectrum of the various colors that steel takes on, during the process of heating which forms “an oxide layer…on the surface” as described on their website. The thickness of that oxidation has a direct correlation to color via the light reflected (interference), and thus you get this spectrum:
Temperatures below 800°F (427°C) produce oxidation colours.
Temperatures above 800°F (427°C) produce incandescent colours