The brand of paint that I use is called Testors. It's a gloss enamel that is sold in hobby stores, and I think that it's intended use is for coloring plastic toy models.
For the fly in the pic, I used a small brush to paint the yellow eye, but used the end of a very fine match stick to dab on the black pupil. When I paint clouser eyes I do the same thing, brush for background and stick for pupil.
By the way, I'm not sure if you're familiar with this trick, but painting clouser eyes in large numbers is done very easily with the use of an old comb that has large teeth. The eyes slide right between the teeth, and you can hold the handle of the comb in one hand and paint with the other. It's a little assembly line of sorts. It's also a convenient place to keep the eyes while they dry.