I wouldn't be suprised if eating catfish made the bass turn a different color. Compare farm raised salmon with wild salmon. The meat from a farm raised salmon will be relatively white if color dyes are not added to their food pellets. The meat of wild salmon gets their pink coloration from eating krill.
Now I grant ya, these coloration differences are on the inside rather than outside but all fish will vary in coloration depending on water color, light penetration, bottom composition, time of year, etc. It seems reasonable that food sources would do the same thing.

Psst... I have a theory about the color red in lures. If red is the first color to fade out, wouldn't it be reasonable to think it would be the first to take on a more natural appearance underwater??? That is why line companies make red(pink) fishing line which was all the rage in the 70's and early 80's.
Hmmm... ;)

Chris