Once they develop you can try foods that contain large amounts of carotenoids, such as Krill--(and of course the pellets)
"Astaxanthin is the carotenoid that gives wild salmon its deep pink or vibrant red color. Carotenoids are fat-soluble pigments that give red-orange-yellow color to fruits, vegetables, egg yolks, the aforementioned wild salmon, steelhead trout, shellfish (e.g., shrimp and lobsters), and the feathers of birds, notably brilliant pink flamingos. Fish and fowl alike get their red-yellow-orange hues from eating large quantities of carotenoid-rich aquatic plants, such as algae and plankton."
Krill consume this algae as well.
