I'm not typically the sort of person to get too bogged down in the "in universe" explanations for these types of things, but Boba Fett obviously painted the armour since originally taking it over from Jango Fett, so the paint would have looked clean and un-weathered at that point too. Anyone trying to say that it was a production mistake to write this in or that it goes against the "character" of Boba Fett to bother with any design aesthetic choices is just ignoring the larger history of this story. I think it makes total sense that he might want to freshen up after all that he has gone through and I really dig the look. You can already see scratches in the paint forming in this episode, so he's on his way towards the classic worn look we all love, just give him some time.