Yes have seen paint marking on some of the original 66 dual exhaust mufflers I've seen, owned or have pictures of. Happen to be all that were produced in the Nov 65 batch that was produced. Not really stripes as observed on these examples but more like spray dots though of course a guy could get sloppy or carried away.
Have seen a green marks on the other muffler(different side) as one might expect but these don't show up as well as the yellow. Have not been recommending or sharing the markings in general since they have not been found in great numbers since so few original mufflers are or have ween out there in good enough condition to see/find the markings.
Sorry don't apparently have a green mark example. Know that there is one up in the attic but apparently didn't take a picture before I put it away
Will have to correct that when I get up there for the Christmas totes in a few weeks.