Glenn, I don't use a primer when painting yellow, white, or red, by brush or airbrush. I use the matt version of each as a primer, usually just one coat, then spray or brush the finish coat in gloss (yellow in this case). The trick is to ensure the first gloss coat is sprayed to cover any 'thin' areas in the base coat, ensuring it is totally dry before the next coat. The final gloss coat is built up whilst spraying, then, when it's still damp, but not wet, a thin, even mist over the top to finish. I always ensure the area is covered fully, by commencing the spray before the 'target', the continuing, ending once off 'target'. This is more exagerated than normal spraying, and allows a better, more even concentration of paint in the desired area.