I wonder if it has anything to do with the fact that the fish on live forage need to be more aggressive to get a meal and display more color as a result. Those fish on commercial food have no need to be aggressive or expend energy to catch a pellet.
It could also be that the fish on live forage are getting some micronutrients that the commercial food lacks. I had the same dull off colored look with a group of RES sunfish that I feed trained last year.
