Most decent quality foods made today contain plenty of color enhancing ingredients, spirulina for blue/greens (not kelp), astaxanthin for red, marigold meal for yellow, etc. But you have to realize that a fish can only assimilate & utilize so much, the rest is simply passed in their waste. As an example, studies performed over the years have shown that as little as 2% spirulina is required to maximize its color enhancing properties in most species studied. (Ako et al) Too much of a thing can also be bad, such as using excessive amounts of synthetic forms of color enhancers, such as Carophyll Pink, or Carophyll Red, to enhance the color red. Too much will make a fish that is naturally yellow, turn orange.
Not all manufacturers will break down exactly what they have added to their feed, or exactly at what concentration, but the higher quality foods have every color found in nature, covered. The rest is up to genetics, and of course everything else that one does when keeping fish in a glass box. Water quality, temperature, hardness, aggression levels, sexual maturity, etc, can all have a major effect on the coloration of a fish kept in captivity.
One of my favorite foods that produced very good results in all colors of the rainbow, has been NLS. I have experimented with adding raw spirulina, raw astaxanthin in the form of Haematococcus pluvialis algae, from a Cyanotech rep in Hawaii, fresh krill from the ocean from wholesale suppliers on the west coast, and probably everything else one can think of, just to see if I could take things a bit further, no luck.
Feed a good quality food, take extra good care of your fish, and their genetics will take care of the rest.
As far as blues etc go, all of the fish in the following link were raised exclusively on a single pellet food. And most of those pics were taken with an ancient $20 point & shoot.
I shut down my last African tank this week, sent them off to a friends fish room where they will live out their lives in his 270 gallon display tank. I got to thinking about all of the various African cichlids that I have kept over the years and started going though my HD for photos. I thought...
www.monsterfishkeepers.com
RD.
Maybe he will chime in.
