So here's the tl;dr version:
To the perceptions of the human eye, the chemical make-up of a plasma is irrelevant in deciding what colour it is. The only important factor is the temperature. The hotter it gets, it moves from red through yellow to pure white. (And if it gets insanely hot, a faint blue - a bit ironic, given our normal perceptions of red as a warm colour and blue a cold one). If you want to know why, my last post will explain it in plenty of detail.
So if you want to paint it an inappropriate colour (anything that is not a natural spectrum for black body radiation), the appropriate excuse is "artistic licence", not "different chemicals".