Complex topic. Much easier asked than answered.

The US Navy published a paint manual called SHIPS-2 in early 1941. It remained in effect (with revisions) throughout WWII. Want to know/understand WWII USN ship colors and painting? Thoroughly read and learn this manual:

https://www.shipcamouflage.com/SHIPS2.htm

Between the end of WWI and when this manual came out in 1941, the standard US Navy color for vertical surfaces was called #5 Standard Navy Gray. That color can be found here:

http://www.modelwarships.com/reviews/books-plans/snyder-short/usn-1/usn-01.jpg

With the publication of the first edition of this manual (January, 1941) the Navy announced that most all ships should adopt Measure 1. That can be found in the manual, in the January '41 edition. That is a dark gray called 5D (almost black) for verical surfaces, with light gray 5L masts above the funnel tops.

So...by Sumner 1941, the fleet at Pearl Harbor was finally in this new Measure 1. The paint materials had arrived, been mixed, and ships all painted.

However...

Also in the Summer of 1941--just as the fleet had gotten into Measure 1--new orders came out for a new color...Sea Blue. And this is where all the angry arguments happen.

After an order like this is issued, compliance is not instant. It takes time for the new color to be made and distributed, and the painting to actually happen. On a most basic level, there is much (very angry) debate about whether Arizona especially had changed to the new Sea Blue, or was still in the old Measure 1. Whichever side you decide to join, you will just make the other side angry with you, and there are fragments of evidence to support both sides.

The "best answer" which can be given is that we know for sure that Arizona was in Measure 1 in the Summer before the attack. So, that paint scheme is "safe." It MIGHT have changed very, very late in the year, perhaps, maybe, possibly.

So... pick one, and Good Luck! As noted below, it is your model. Paint it whichever way you feel is correct.