Spirulina and anything made from krill. Spirulina helps bring out the reds in fish.
Hikari has foods that usually brings out the color.
I feed Hikari Marine-A and Ocean Nutrition Formula 2 pellets to my f/w fish because it's way too much food for the s/w tank.
Anyway, these Silver Dollars I had for more htan 5 years colored up around the fins and their black or red spots are more noticable. I have 3 distinct kind of SD just sold under the generic SD common name.