ok here is one or two... I have seen two basic color schmes of the S Boats... one is in an almost white grey hull with a aircraft grey (with a touch of blue) decks... don't know the actual german color codes, just matched pics I found as best I could...
To a S boat with an all over aircraft grey type shade of grey (with the touch of blue) I have included a review of the model here: (note the bottom hull color is red with the black demarcation line here, the kit says all anthracite grey for the lower hull... I have found examples of both on the web in WWII pics... you choose... I liked the all anthracite grey bottom)
http://hsfeatures.com/features04/s100dj_1.htm
http://modelingmadness.com/reviews/misc/spahrs100.htm
(check out the links at the bottom, the last one has a reference to the exact boat in the kit!)
I'll post more if I find em... this was definitely a NICE kit to build! took awhile.. but nice!!!