If you use a food with astaxanthin, it may bring out and intensify the red.
Astaxanthin is a carotenoid found in algae among other foods that makes salmon red and shellfish red.
I use combination of NLS and Hikari Bio Gold+ and occasional FBW and my fastaes love them but more often than not, water quality will bring out their colors.
Its all in the genetics and husbandry. If it cones from impressive parents and is well cared for it will turn out a beautiful fish no matter what. Food wont do a whole lot but agree with Duanes on astaxanthin in the food.
krill, for color earthworms growth, pellets for their vitamins carnivore /omnivore u know and blood worms frozen cause they love them. but frozen krill for color the reds.