I thought it was an interesting wrinke to the character. In TFA you basically had “Palpatine, but again”, whereas showing him in gold in TLJ implied that he was opulent and showy, as if he was narcissistic and wanted to present himself as ostentatious. I don’t see any good reason why a Sith wouldn’t choose to show off in gold, especially since they’re not doing the ‘hiding in the shadows’ thing any more. Compare to Ludo Kressh: https://static.wikia.nocookie.net/swtor/images/f/f5/318991-36149-ludo-kressh_large.jpg/revision/latest/scale-to-width-down/340?cb=20130527154330