The box art is Measure 12 mod. The instructions call for Sea Blue splotches on the hull over 'Dark Gray", and I guess 'Dark Gray' splotches over 'Neutral Gray' above the main deck. Problem being that "Dark Gray" and "Neutral Gray" aren't USN colors.
Measure 12mod uses combinations of three colors on the verticals in almost all cases. My own choice was to use Ocean Gray on the hull as background and Haze Gray on the verticals above the deck as background, with Sea Blue splotches below and Ocean Gray splotches above.
So if you choose that route, finding Tamiya equivalents for those colors isn't too difficult but you are right, they are mixes.
Or, in acrylics AK makes USN set #2 with all you need.
Other measures to choose:
https://www.shipcamouflage.com/fletcher_class.htm
Bill