I assume that you properly prepared the frame for painting by removing the old paint completely and applying sandable primer, and that you are using LACQUER and not enamel or epoxy. If not, you'll need to do so before proceeding.
As far as base coats, the primary function is to have an even color so the top color coat doesn't look splotchy but there are some colors that benefit from a particular color base. When I paint frames I always use a white base under opaque colors. If transparent type finish (like candy apples or metal flakes) I use white, gold, or silver depending on the desired final hue. I think I even used black one one frame a long time ago.
Of course, you need to remember to apply a sufficient amount of clear coat over the color to protect the finish and maintain the hue.
If you were just going to buy a $6 can of paint and have at it, I wish you would reconsider. It takes effort and time, as well as a reasonable investment to paint a bike even if you just use spray cans.
