Food has very minor effect on colour, just feed a good quality pellet. Supplement with bugs and frozen. I would bet most of the colour enhancer specific foods rely more on a random concoction of ingredients in higher than necessary concentrations (xantiia red and ceratine or whatever they are) than actually a healthy balanced diet, add to that fancy packaging to draw in the buyers
If he is infact healthy and your tank has plenty of surface agitation and clean water then I would look at stress, does he have caves for some alone time?
Also consider FH have Midas traits and along with many other centrals their colour changes continuously as they grow, Midas and rd in particular generally grow lighter and lighter as they age.
What's your water change schedule, I would stress that barely anyone does enough, minimum of 75% but ideal fin level per week every week.
Read up on 'nitrate creep' and think of most aquatic habitats having well below 1ppm.