Color loss is usually an indication of malnutrition. What does his diet consist of, and what are your water parameters. Specifically, nitrate, ammonia, and salinity levels?
everything is within normal parameters and we feed him a variety of foods that are suppose to enhance colors flake and frozen pretty sure it is not malnutrition as he has tripled in size since we have had him (about 2 years) right after we got him his face turned white but lfs said not to worry about it (they medicated him for us)
it sounds like the diet is the problem. if anything , you should be feeding him tons and tons of greens. seadweed and such. they are herbivores. they will eat meaty stuff, but they need their greens