It's showing no color because it has released all it's zooanth somthing something somthing "can't remember how to spell it" due to it being under too much light or not enough light for a a period of time. That is the stuff that lets the coral convert light into the energy it needs to live and also what gives the coral it's color. They can be brought back with care and they will develop color and zooanth somthing somthing something, and the coral could be healthy again, but the chances are very very slim. Now put on top how tough it is to keep goniopora, and that piece is near doomed.
A good rule of thumb when looking to buy coral is, if it's white or "crystal", stay away, it's bleached and not healthy. There are no white corals that we keep in our aquariums.