I have two Perc Clowns that I bought a few weeks apart from different stores. The 2nd one was quite a bit lighter/faded in its colors as compared to the 1st. I've been feeding brine shrimp soaked in Kent Zoecon to them for the last month and the colors on the lighter Perc have improved dramatically and the other's has darkened even more. Of course I can't prove it's due to the Zoecon as it could be just my overall water conditions are better than the store's. But it' pretty strong circumstantial evidence.
I haven't had any clouding problems either, but I have wondered about the long-term effects of continually feeding them Zoecon enriched food, I am thinking of backing of from daily to maybe 1x or 2x a week.