That's a very debatable question.......
from what I learned, sitting back and laughing, during the three month flame war at another site, famous for flame wars.....
The wings were... 1. panel lines were filled and sealed and wings were painted. Even the bare metal ones had silver dope on the wing. Only panel line actually visible in the torrid of photos flashed before us usually showed only the access panels for the guns. I say usually, because some photos did indeed show unfilled panel lines. Most rivets were either invisible or barely visible in the most of the photos, but again a few showed them rather clearly, which started another round of name calling and insults.
Fuselage were....1. either highly polished, somewhat polished, or not polished just weathered metal, again supported by the colorful langauge, endless insults, and photos posted, depending on the time frame, and care and mantainence of the ground grews. Again, some photos posted showed what clearly appear to be a silver lacquer finish, which again started another round of more insults, name calling, and language that blistered even this old swabbies ears........
Now the above was for a simple question such as you asked, about WWII P-51's.
Now I'm no expert in the P-51.... not by any means, and I'm sure we have quite a few members here who know more about it than I do, but common sense..... yes ... we once had that..... would tell me that by the time of Korea, baremetal, and corrosion didn't mix too well. Might look pretty for a photo op, but in reality, corroding airframes fall apart at the wrong times, so I believe by Korea they were probably painted in a protective silver lacquer. Maybe not all, and maybe there were a few ground crews who had nothing better to do, between dodging bullets, mortars and attacking North Koreans and Chinese to take the time to polish the pilots P-51.
OH... the main spar in the rear of the wheel wells ... that was zinc-yellow...... the rest of the wheel wells were doped silver, and the doors dropped open as hydraulic pressure dropped, so in reality....... you can have the doors in an up position, or a down position, or any place inbetween.
Looking forward to seeing your P-51.....
Have fun.... build a model......
:-) :-) :-) OH... I apply metalcoat with an airbrush, but it can be brush painted also.