I've found one aerial picture of USS Maryland BB-46 and USS Iowa BB-61 but it's from 1945. Deck looks rather very bright on BB-46. The one on Iowa seems to be a little darker(
http://navsource.org/archives/01/046/014661i.jpg)
Also here's a good link:
https://en.wikipedia.org/wiki/World_...3:_battleships
According to the informations from wikipedia, deck color on Colorado-class battleships should be Ocean Gray 5-O.
I have no idea which one would be the most accurate option... From the aesthetic point of view I'd go with natural wood.
Anyway, here's the WIP update. Hull is basically finished, I just have to add some tiny details.