255 Mazao's truth about time-travel 2

According to Little Bowl No. 2's description, the Catastrophe Demon appeared as a giant humanoid monster wrapped in black flames. The face within the flames was not discernible; it might have been a monster made purely of black flame.

Humans, after undergoing Sin demonization, usually transform into a monstrous form, similar to how abnormal beings turn into goat-headed Demons when exerting their full power.

In the data I have come across previously, there was no specific mention of the color of Xuanming's flames. Seen from another angle, the absence of specific mention implies it wasn't a particular color. However, since Sin demonization had occurred with a drastic change in human form, it wouldn't be surprising if the color of the flames changed as well.