How long have you had them in your system? They do like lower light but sometimes if they get very, very little light they'll lighten up like that as well. If they're new, I'd move them to a low light spot and see how they do. It'll take a lot longer to do damage in low light than it will in high light.
On the other hand, I have a similar favia that turns that color whenever it gets annoyed or moved. It's one of my faves but it is really, really sensitive.