When I ordered light kit from AHS, I put an order for two 6400K bulbs to go
in it.
6400K+6400K combination seemed too greenish and I ordered couple of Red/Blue
bulbs. In additon to that I have Red/10KK and 4700K. I did a quick
comparision of different
combinations. I didn't include 4700K in any combinations. I am quite pleased
with 6400K + Red/Blue combo.
http://www.culbertfamily.com/jenya/aquarium/lights/

Jenya