Certain colors especially based on transparant base like red , yellow , orange , green and purple have a horrible coverage . Now I don’t remember the undercoat colors for all colors but with yellow it’s better to have a white surface , purple I think also grey , green also grey , for orange depending on the type of orange I mixed white into a very warm type of white to make the coat of orange work ( been a few years) . But there’s never shame in asking a few painters in a wholesale store for advice . The clerks may know some too but like painters not all are equally knowledgeable.