I find that most of the dull looking corals we hear about with these fixtures are from lack of proper acclimation. IME, it takes months to get a coral to color up to it's full potential under these particular fixtures, no matter if you use a RB or similar fixture with multiple colors, or a straight blue and white one.
just can't handle the fixtures at full strength. I am growing montipora and keep anemones under a Tao fixture with just the blues at about 80%. Turn it up any higher and the anemones hide.
Even going from one LED
unit to another, potency differs.
I have a 250 watt halide fixture set up over one of my sumps with a 20k lamp in it and The same corals look 100 times more colorful and more florescent under the Tao units I am using.