You could experiment and spray over something black then something white and see how it turns out. Usually if you spray a color over white it becomes brighter. Spray yellow over a black base and watch what happens. It will be a lot darker than if you spray over a white base. It will also require more coats to cover. Same with neon colors. I recently sprayed Sunset pearl orange over white base and it turned out real real good. Looks killer in the sun. I sprayed Heathers helmet and a junky old hood that I had just to see if I liked the color. You can see those pics here.
http://www.pro-touring.com/forum/sho...ght=girlfriend
It was the first time I painted flames on anything.