This is a phosphate finish cyq P.38.  It is well known that Mauser used a phosphate finish on their late P.38's.  It is also well known that Walther used some phosphate small parts on their late P.38's. What is little known is that Spreewerke experimented with the phosphate finish and a very few guns have turned up as proof.  The German style phosphate has never been reproduced by anyone after WWII. Warren Buxton has examined this gun verifies its' authenticity.