John,
I use enamel paints from my local hobby shop. I typically try to match the dominant blank color or try to get close. On some, I'll paint the inside of the blank in a lighter color or a metallic color (gold, silver or copper) to try to help "pop" a color. On others, I'll paint the inside of the blank a dark color to help enrich a color.
For many, it's a little trial and error until you get some experience. There are some threads around where some folks have painted different color bands on a wooden dowel and they'll insert the dowel to try to get an idea of what may work.
By and large, I believe anyone will tell you that it is going to take a little experimentation on your part to see how it goes.
Happy experimenting to you.
Matthew