Documentation aside (I've never seen any on it), there was a gray/black paint scheme used by modern nuclear submarines in the 60's/70's. It was, as you described, a black hull with the vertical sides of the sail in a medium gray color. The fairwater planes are black top and bottom. It was colliquially called the "Pacific" or "West Coast" paint scheme. The basic idea was if you see it from the top, it would be all black. On the surface, the vertical services would be gray and theoretically less visible. A twofer!
It can be difficult to tell, especially in black and white pictures. Heavily weathered black can look gray.
I've seen pictures of 585, 594, and 637 class boats with it. Navsource has a mess of them. Queenfish, Haddo and Scorpion are a few that have pictures. As a matter of fact, in 1973 the Navy published my favorite poster ever - Queenfish at high speed in the Pacific Scheme with the caption "Pride Runs Deep". You can see the black on the top of the sail and the top of the fairwater planes.

Apparently it wasn't unique to SSNs. Here's a picture of an SSBN in a close relative of that color scheme (SSBN 630 from Navsource)
https://navsource.org/archives/08/616/0863012.jpgHowever, in my time in the Navy (1976-1992) in San Diego, Charleston, Norfolk, and New London, I've only seen all black paint schemes on any class of submarine excepting NR-1. I still haven't found a picture dated later than 1973.
Underhulls are typically red from the max beam to the keel down the full length of the ship. Ships with towed array fairings will typically have the red go to the sonar dome which is totally black. I believe that ships with SHT, and newer classes of submarines, are all black. Of course, a bit of research on the boat you're building is in order.