What causes flame color? I know light color corresponds to photon energy which is related to electrons relaxing from a high to low energy state. I'm not sure how to conceptualize this situation though. My professor was heating a 0.8 wt% carbon steel rod, in austenite phase, with a blow torch until it started glowing. I assume it was still in the austenite phase. During the heating, the flames from the blow torch were blue until the metal started glowing orange. At this most of the flames changed color to orange. There were still some blue flames at the outlet of the blow torch but those that were past the piece of metal were all orange.