I believe that the coloration of the corals may just be changing to fall in line with the intensity and color spectrum offered by the lights. Don't quote me on this, but I think:
If the zoaxanthallae were moving, you would see one coral releasing it in stingy formations,a nd the other coral would pick up the zoaxanthallae from the water column. The coral would release it only if the lighting were not strong enough to provide enough energy for the coral to sustain the energy requirements of the zoaxanthallae...basically if the zoaxanthallae were taking more energy from the coral than they were giving. At this point the relationship between the two animals become parasitic rather than symbiotic, and as such the zoaxanthallae is expelled by the coral in ana ttempt for the coral to survive based on the available energy.
Also, I think that the coral has the coloration, and that the zoaxanthallae merely provides the energy to the coral...more energy, brighter coral. But I don't think the zoaxanthallae itself has a "color morph"...ie, I dont think a green mushroom has green zoaxanthallae...rather I think it has normal zoaxanthallae (which I think is tannish) and the coral itself is green. Thus zoaxanthallae taken up by coral from the water column would only brighten the inherent color of the coral that takes them up, rather than change the coloration fo the coral to fall in-line with the accpeted zoaxanthallae.
My guess would be it is just a color change based on the lighting. If all the lighting is actinic, then it may be highlighting certain colorations to your eye based ont he spectrum, and the ccorals may itself respond to the offered eneregy source in some manner.
Again, don't quote me on this, but this is my thinking, but I am not saying this is correct!
Stewart