that fish will seriously look deadly when full grown if properly taken care of or the right person has it. I wouldn't second guess that fish if you are looking into having a monster !!
I feed NLS, but its up to you; you can mix it up as well.
I like that fact that its an all natural, color-enhancing staple diet; but others like the fast and quick growth of Hikari.
In addition to containing whole parts of a meal and color enhancing ingredients such as Spirulina, I also like how NLS contains garlic or a mega-dose of garlic that acts as a natural anti-parasitic; prevention.
Color mainly has to do about the genes of the fish, and clearly yours has some great genes.
so no matter what you feed him, he will be a stunner.
Just don't overfeed a food that has a lot of fillers or feed live food with the risk of developing a parasite even in a hardy fish.