The Shipcamo site is your best bet, they are the US partner for paints to White Ensign Models (WEM). These guys THOROUGHLY research paint, then have it custom blended to their specs. I just bought a small tin of "Dark Gray" for my 1/72 Gato, as a test, and I was surprised to find it is very, very dark, especially compared to the Humbrol USN equiv I bought. So I'm glad I went to WEM.
I've seen some excellent U-boat builds and paint jobs, but some funny shades of gray because people used average grays. Worth the effort I think to use correct colors.
The 2-tone gray and black was Measure 32/(lots of variations in the slash part), popular in about 44, maybe starting 43, though it was chnaged in late 44/early45 slightly. Dick O'Kane noted that the new paint job (as opposed to the Measure 9 all black) was excellent camo, he and his lookouts couldn't see a rendezvousing sub until they were quite close, even in daylight.
Keep us posted on the build
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