One thing I want to mention about doing pin striping and that is pin striping specific paint has more pigment so a couple of applications is not necessary so the paint color underneath is not visible. There is nothing more problematic that doing a nice job but the paint doesn't cover well enough and you can see through it to the base color. If one thins down regular paint so it flows more easily, then it can be too thin to cover the undercoat color adequately.
House of Kolor makes a pin stripping pain that comes in a very small paint cant. Of course it is expensive but they come in a variety of colors.