The SHIPS-2 painting instructions for Measure 22 called for the Navy Blue to be painted down from the lowest point of the sheer line (the fore/aft curve of the deck is called the sheer). The upper edge of the blue was to be parallel with the horizon (i.e. it didn't follow the sheer).
See the SHIPS-2 painting instructions at shipcamouflage.com
The hull above the sheer and the vertical superstructure surfaces above the blue were to be painted 5-H Haze Gray. Note that the WWII USN colors were based on a purple/blue sustem and that Haze Gray had a decided lavender cast. 'Accurate' colors are available from White Ensign in their Colourcoat line of paints (enamel) and the Model Master Acryl II Marine (out of production but still available) in acrylics. Tamiya's Haze Gray recommendation is for their own paint line which is a neutral (i.e. not tending toward purple/blue) gray.
Photographic evidens at the US Naval Historical Center shows that the wooden decks were painted/stained blue. 20B deck blue is your paint color. Steel decks, turret tops and the tops half of round items (i.e. gun barrels) were also painted to match 20B