This would be for a VIIB, my current and most favorite sub...
Deep blue below the waterline and slate blue above with a black camouflage pattern taken from Wolfehunter's winter camo skin for the VIIB-VIIC...
Full-sized image linked here...
VIIBwinter2.jpg
I don't know if the camo pattern would look best in black or another shade of darker blue or the same shade of blue as the lower half of the hull.