As pointed out by others, the german torpedoes were generally not painted except for the heads (both warheads and exercise heads). Also, I believe that some G7e's used on midget submarines might have been painted to ensure proper camouflage of the vessel (I haven't seen any colour-photograph to indicate which colour though, but black/ dark blue/ dark green would be a godd guess - camouflage was of course just as crucial on land as in water).

Regarding the T5 warhead: The front part with the seeker-unit ("ear") was originally painted dark grey and with (at least some of) the text/ stencils in red. The norwegian naval musum has one of these in it's original shape at display (I have photos available).