The Luftwaffe paint finish was a smooth, semi-matt, and resistant to staining and wear, in general. The ID colours however, on the cowling, were applied with a distemper-type coating, removable by washing with petrol (Gasoline). This finish was very matt, and extremely sensitive to the slightest stain. Any muzzle blast would very quickly discolour the surrounding areas, having the effect of burning in to the distemper, making the staining look even worse.
There was a particular exercise I was on, when our Land Rovers received a distemper wash. After firing only a few short bursts from a GPMG, it took about an hour to get the effing stains off !!