HWaA the dipped pistols will have a black jelly bean luster that will hide the original finish. They also dipped over the S and F so it will appear to be black and not painted. Thirdly the locking and pin at the rear will appear dark blued but not to be confused by the light bluing of some late Spreewerk locking blocks and pin. On the Walther and Mauser P.38's the locking blocks and pins are always in the white unless dipped.
I hope this was helpful.