I've used Testors model paint to do dots. The trick, for me, is to degrease thoroughly, and let each coat dry for 24 hours before adding more.
One of my very favorite sight pictures on a 92 is a .270 Wilson Pepperoni sight, and the front sight dot painted with Testors yellow fluorescent. I see that setup as good as any fiber optic I've tried. It's one of the reasons I just really don't get too worked up about fixed front sights anymore.