Is this a full auto? If so, your only concern is that the information on the Form 4 matches the gun. It's possible that it was built from parts and is not original to WWII, but is still on a Form 4, but if it qualifies as a C&R gun, you're good.
The cam piece is a different steel from the sheet metal of the gun, and the blue will sometimes go purple because it accepts the blue differently. Lugers parts are frequently this color, and it's always possible the cam was replaced. For a C&R gun, I wouldn't worry about that.
Without better/more pictures, it's difficult to say more.