A wide mix of foods. Live black worms, live blood worms, ect. Good water conditions. Ive also noticed sometimes different kinds of lighting make the fish look different. I.E Led lighting makes some fish pop, while others look dull in it.
I breed a batch of these a few months ago. They are just starting to get over 1" and haven't hardly yellowed up as much as the full grown adult breeders, but the markings on their finnage is prominent. You might have some younger ones that just need to grow into their britches still.