They could be original bakelite grips (but don't belong on this 1938). If you're considering buying this pistol definitely get better pictures of the grips posted. They could be fairly valuable.
I believe my 41 byf does have original black grips and here's a link to detailed pictures of the inside and outside so you have something to compare to.
http://forum.lugerforum.com/showthre...threadid=16922
As far as the "two tone" effect, my 1938 receiver has a "plum colored" brownish blue like what I see in your photos while the barrel is much darker blue.