I came across this article while researching colors for my USS Arizona: http://archives.starbulletin.com/2006/12/07/news/story04.html . According to it, the Arizona and other US battleships were painted a medium blue at Pearl Harbor, not the dark sea blue I was going to use. The information is based on a recently-discovered document by Admiral Kimmell, in which he prescribes US battleships to be painted what was called 'Mediterranean Blue'.

Based on this, would you discard your dark sea blue for a medium blue, as with the USS South Dakota?

I recall this coming up some years ago (more than 10) and I think, although it wasn't really my period, that the conclusion was that the battle line was Ms1, which was dark grey with light grey spotting tops. I used to know the official colour designations but my poor brain has filled up with other stuff and info like that which I didn't need to retain as I had it stored elsewhere was overwritten😟

I haven't followed the debate since but the Ship Modellers Mailing List is an excellent source of knowledgeable people who are more up to speed on it than I am.

I note that you use the phrase 'was to be'. It may well have been intended to have been changed (Ms21, the overall Sea Blue scheme came later as defence against aerial observation) but the photos I have seen of battleship row rather suggest that Ms1 was still in use in December 1941. As I say, I'm no expert though!