A too-thin (or too-small) front sight will remain a too-thin (or too-small) front sight, no matter what you do.
Painting the entire rear surface of the front sight bright red will help a little. (Fluorescent paint is not necessary.)
Go to a drugstore, or even a beauty-supply store, and buy a bottle of bright white nail "polish" (cellulose enamel, really) and a bottle of bright, fire-engine red nail "polish."
Clean your front sight very thoroughly with alcohol, Energine, or some other cleaner-degreaser. A Q-Tip works best.
Using the brush inside the cap of the white nail polish, carefully dab a coat of the stuff on the rear surface of the front sight (the part that you see through the rear sight). Let it dry for at least 12 hours. Use a very sharp knife to cut or scrape off any excess paint from the side surfaces of the sight blade.
Re-coat the sight with the white nail polish, and let it dry for another 12 hours. (You probably didn't have to scrape any off, this time. Right?)
Now apply two coats of the red nail polish, letting each dry for 12 hours.