I don't personally play Space Wolves but if I did I would probably go for more of a Gray color instead of the baby blue/ bright blue you see sometimes. Your best bet would probably be browsing the paint section of
GW's website and just picking what you think looks good.
http://www.games-workshop.com/gws/catalog/landing.jsp?catId=cat730002a&rootCatGameStyle=paints-tools
They also have "painting guides" where they recommend color combinations for different things. For example, for Space Wolves they recommend:
The Fang -> Nuln Oil -> Russ Grey -> Fenrisian Grey -> Etherium Blue ->
You could probably mix some black or dark grey into some of those colors for a darker look or just add some extra Nuln Oil wash.