I've tried 100% pure spirulina flakes with my frontosa's and other african cichlids when they were smaller, from this site
http://kensfish.com/kensflake1.html (midway down the page under "Pure Spirulina Flake").
My fish were on NLS prior to using it and were fed NLS concurrently with the 100% spirulina flakes, so I didn't notice any change in their blue hues (which were already excellent, and possibly indicates the spirulina content in NLS is enough). Ceased using it due to cost, small flake size, and the fact that my fronts were getting too large (larger frontosa's might not go for it due to the small flake size and will probably prefer pellets over them). My mbuna's loved it, but they're not particular.