The stern of the Oscar IIs are painted the same as the front, with red on the bottom half and black on the top. The lower half of the planes are red and the upper half black, same with the shafts. Here's a picture of an Oscar II in drydock with a fresh coat of paint, probably K-186 Omsk
If you want to portray a more weathered Kursk
, this picture might help.
I don't think that the lower bow, where the bow sonar window is, is colored silver though. In all the drydock pictures I have seen of Soviet and Russian submarines, the sonar windows are always red, usually a slightly lighter shade as the sonar window is made of composites (usually GRP), a different material than the rubber coating the hull. Here's a picture of K-266 Orel
I'm guessing that you got the impression that the sonar window is silver based on the 1/350 Zvedzda Kursk kit, which is unfortunately a very inaccurate model. I recently replaced my Zvedzda Oscar II with a resin model from Polar Bear Models out of Severodvinsk (http://www.submarines.zx6.ru/
), and when I compared the two it was like night and day. The Zvedzda kit was blocky and highly inaccurate in many ways (hull shape, direction of propeller blades, length, number of lower rudders ect.). Although the Polar Bear kit is about three times more expensive, it is well worth it. Free Time Hobbies sells it and other Polar Bear kits (http://www.freetimehobbies.com/PB3527.aspx
). I hope my response was helpful.