nice model!
lots of detail in a small package!
when you say "shields around the props"- do you mean Kort nozzles? Some of the Type II (C or D, I can't remember which) had Kort nozzels around the props, which look like the nozzles that were found on some of the German Seehund midget submarines. (If this explanation isn't clear, think of the shroud around the propulsors on a SSN-21 Seawolf...)
Most U-Boats had their wooden decks painted dark grey. Grun, lichgrau, dunkelgrau are all decent colors to use for U-Boats. Grun is sort of a green/blue tinted gray that shows up on lots of type VIIs.
Might I suggest you get your hands on "vom original zum modell uboottyp II" as a great reference for the Type II boats. (ISBN: 3763760237)
Additionally, there a book on the Type II and it's role in the Black Sea that would probably answer your question about the camo (although I believe you are correct that these Type IIs did use two color camo...)
Quidquid latine dictum sit, altum sonatur :)