Live foods are the best food for killifish, period. They may be cultured or collected from a "clean" pond. Scheel and others showed they eat ants, flies, aquatic crustaceans and worms.
Its important to note that the insects that fish eat consume pollen, thus fishes obtain exotic phytonutrients vital to pronounced body color intensity. "Color foods" garner some disdain yet merely supply molecules such as Astaxanthin and others required in trace elements for both the fish health and well being but also optimal pigmentation.