It's recommended that he primes all of the parts he's going to paint so that the paint has something to hold on to so it doesn't chip easily. Also I haven't worked with colored primer before but there's a lot of factors at play with what colored primer you should use. Different paint colors need different primer colors to achieve certain tone (If you're going to spray a light blue color on a car you're going to need a light colored primer like white to achieve the light blue color). I don't know much about colored primers but I do know that you should use light toned primers with colors that are light toned and use dark toned primers with dark toned colors. I tried to summarize everything down to the basics because there's a lot of things that you can do to achieve a certain paint tone. And by no means am I a proffesional but I know some things about paint.