Ed,
I found that the rivet gun leaves a mark on pre-painted pop-rivets . I
installed plain rivets then used a small bottle of almond color appliance or
sink touch up enamel. It comes with a small brush in the bottle that is just
the right size - one dab on the rivet head coats it quite well. I even keep
one of these little touch up bottles in the trailer so that if I need to
replace a rivet on the road I can put a touch of paint to it right then and
there.
Forrest