I don't know when you started your tank. But if you're implying 150 days and they weren't light-acclimated, then your lights may be too intense and the zooxanthellae are being expelled, hence the color change. I would lower the lights to maybe 25% of what they're used to and make sure you continue to feed. Then step up the lights every week or so until you're back to previous levels.
However, if you feed a lot, they may be simply excreting. Depends on whether they close up daily and then re-open, or if they just stay closed over the course of several days.