Everything that contains Carotenoids are good color enhancers in fish and other animals, even for us humans, eat al lot of it (Carots or Tomatos) and go sun bading you will see your tan change in color.
Spirulana is a Blue Green Alga sp. that next to Carotenoids also contains Fycocyanin protiens, that are also pigments that give it that blueish color. Some carot sp. that are purple likely also contain Fycocyanin to get that purple color. If this in particular will enhance blue colors in animals i do not know.
But since both are healthy food supplements and that anything containing Carotenoids probably also contains a dose Fycocyanin it can not hurt. 🙂
What you feed should be healthy and beeing healthy is the best color enhancer there is.
Carotenoids are also in crustaceans such as Dapnia and Brine shrimps etc. That feed on algae.. Feed that a lot to your fish and they be very heathy fish.
