I love the natural brown interior, with a black or dark blue exterior.  Even with white it looks pretty sweet.  But in my honest opinion I think Silver gray would look best with black or gray interior.  In fact I dont even think that a natural brown interior is available with a silver gray exterior.  You shoud check out bmwusa.com and build your own.  They don't even give you that option.  Or call the dealership and ask about that.  Good Luck!