Albert,
I believe that the darker color at the rear of the extractor may be due to lighting conditions at the time the photograph was taken. This area appears to be to the left of the light source and would be somewhat in a shadow from the hump on the breechblock.
While it is certainly possible that the extractor and grips screws have been refinished, I don't see how it would be possible to determine that for sure.
Is there some test that could tell us if this has happened? I know that Tom Armstrong does some oxidation testing to determine the authenticity of the finish on Navy Lugers, but I have never heard of this type of testing being done on strawed parts or fireblued parts...
just my
