Doing a bit or research for you ...
http://www.navsource.org/archives/01/013546b.jpg
This photo of the Texas shows her 5-inch guns to be painted Navy Blue (5-N) to match the exterior. Measure 21 has a direct lineage to Measure 1. There are no easily locatable photos online of the Arizona in Measure 1 showing her 5-inch guns. However there are seveal paintings of the period which do not show the guns sticking out like a light sore thumb against a dark background. IMO you can safely paint the gun barrels and mounts in your choice of Measure 1 color. The breach mechanism was likely left gunmetal, or bronze for operability.
What is more telling from this photo is that the interior bulkheads and overhead are not painted blue.