20-B Deck Blue is the standard regulation color for decks and most horizontal surfaces in WWII USN ships, though there is some variation depending on the specific camo scheme involved. The Deck Blue would also wear off after a time, and I've seen color photos of WWII US battleships with the blue worn off from weather and crew foot traffic and the underlying wood deck showing through.
After having to hand-mix Deck Blue for years, Poly-S now makes a "Weathered 20-B" in their US range of colors that is quite nice.
The Japanese used a dark brown-ish linoleum on the metal decks of destroyers and other small vessels to dissipate heat, and had wood decks on larger ships (there are numerous accounts from US flyers of looking down and seeing the tan color of IJN decks.) I usually use a medium-brownish-tan color for IJN decks large and small and call it good, though I also have a number of DD's that are just overall grey.
I'm not as familiar with the European navies. The Germans definitely had light wood-colored decks on some of their larger units, and camouflaged the decks on others (Tirpitz in her Norwegian lair,for one.) One book I have says the Brits used a color similar to the US Deck Blue on their ships. There is at least some photographic evidence that Italian ships had naturally-colored wood decks on their larger units, along with the well-known "barber pole" red and white air recognition markings. The French: I couldn't tell ya.
