Foods with astaxanthin enhance (i.e. deepen) red/orange/pink coloration, and foods with spirulina in them are supposed to enhance blue/green colors (and according to one company in Japan, yellow too). Basically, the more of each of these two color enhancers you add, the deeper and darker the coloration. Between the two, you should hit just about every color. There are other things (like beet root, for example) that enhance coloration too, but the astaxanthin and spirulina are the most commonly used in the hobby.Is there something for other colors like blues, purples, and yellows?
As a note here, in a study on clownfish coloration, the preferred amount of astaxanthin (as determined subjectively by 6 pet store owners/managers) was 400ppm as determined by the dry weight of the food.