As you say, they go a grey colour but that's usually only the tiles themselves. If the hull is directly painted, or mastic is used to fair in tiles or sonar apertures, then it tends to stay black. The pic below shows good examples of both.
I'm afraid I couldn't tell you what colour the propulsor rotor is - it's not my part of ship and they're usually covered in dry-dock.
The other colour you need is rust where a tile is missing - the pics of Spartan in Brazil are a good example of that!
