Yes, I do have a hint, and I just found it myself. I had the same problem, I could paint nearly anything in the cockpit but not the markings on those tiny instruments. Yesterday I tried something and it worked beautifully.
If the plastic is light colored it's very easy. Put a drop of thin black paint in the instrument bezel and let it dry thoroughly. Take an X-Acto knife and lightly and carefully scrape the black off the instrument markings, then put a drop of Future in the bezel to simulate the glass. That might take a couple of coats of Future.
If the plastic is dark, put a drop of white enamel paint in the bezel and let it dry thoroughly. Then come back with a drop of black acrylic paint. The black acrylic wil scrape off easier than the white enamel.
Maybe people have been doing it this way forever, but I just hit on it and it works perfectly for me.