I don't think he really looks like Prince Demande at all. The similarities start and stop with the white hair. That's it, imo.
At first when I was watching, his new look sort of bothered me but by the end, I actually liked it. The all-white costume probably represented how he seems to be the least affected by Beryl's brainwashing and therefore the most "pure" of the Shitennou in PGSM.