So I did the sketch in Medibang to figure out the colors, just colored in first with his og color scheme(or an approximation of, I kinda just eyeballed the colors since I haven't remade his reference yet) and used a few overlay and multiply layers until it looked good enough on a dark background.
I would've done this step in Krita if it weren't for the fact the overlay layers imo are kinda meh in Krita, i dunno they just don't give the same effect as in Medi, along with the add layer
Finished pic here: https://www.weasyl.com/~idriveraddsheep/submissions/1919629/ash-red