Improper light acclimation will cause them to bleach. For example if they are ina tank with 175 watt halides and your tank has 250's, without acclimating them, they will bleach.
Another reason 'corals' bleach is not enough lighting. I do not know what a people eater is, and I don't know what else you have that's not bleaching to know.
Placed to far from the light source.