Two comes to mind White fingernail polish, White metal marking paint with a clear coat enamel. These are just off the top of my head and no experience with the use / abuse of the paint, just from the experience of a welders helper and metal marking both temporary and permanent.
Use a cotton swab/q-tip with brake cleaner on it to clean out the "hole" where the paint lays, then once that dries, use a toothpick and use white fingernail polish, dabbing white paint in the "hole" until it fills in nicely.
Just remember if you wipe it down with hoppes 9 the paint will come off.
Thanks for all the input. I do use Hoppes 9 to clean the gun so that might explain why the original paint fell out. I don't have brake cleaning solution and wondering if mineral spirits or fingernail polish remover would work just as good.
I've done the glow in the dark paint, I went back to white dots, the glow paint would only glow for 10 mins tops, when I went back to white I actually pulled the white dots out and used white hobby paint to fill it back in