Try_hard
Why not leave the eye "white"? having an eye like that is unique, and if he came back to his world, he would invent something. I went to research the Byakugan and I think you could have given the pure Byakugan that is from the Otsutsuki, where the eye is not white but it is light purple, and has more abilities like prediction (Demonstrated by Momo and Ura), ability to see things that have already happened (Demonstrated by Kaguya), Absence of Blind Spot (speculative), the white Byakugan is weaker because the Otsutsuki lineage was mixed with humans (I found this theory on the wiki and I thought it was acceptable, that would also be better already that Byakugan always becomes useless, like it's "only" a 360° view but it has several techniques and better skills in anime, in one piece from the grand line everyone has a "Byakugan" you can even read the future there ). Apart from that you can probably make him pay points to evolve into Tenseigan. There's also this part of the theory but I found it useless : The Golden Byakugan is a mutation, arising from the amplification of Otsutsuki's DNA by the genes of another Otsutsuki (Momoshiki - Manga and Anime - and Urashiki - Anime). This only occurs when an Otsutsuki absorbs a large dose of its own species' genes, which, by the "Otsutsuki Nature" itself, becomes a kick to a series of genetic and consequently physiological modifications, one of which would be the presentation of the Golden Byakugan. , which fits like a Pre-New Dojutsu (Same Dojutsu + new skills), i suppose prediction abilities aren't this one's forte, but (speculation) all fighting and investigation abilities are monstrously amplified, the user could cast Genjutsus with it, could disrupt Chakra Circulation in order to paralyze targets, as well as give a charm walk with golden eye.