Bent, I'm an SPS noob myself but that appears to be the opposite of bleaching. Not sure what you would call it. From my experience bleaching is too much light, that however looks like it doesn't have enough which is understandable with all the above branches blocking the light. My green slimer did a similar thing during my whole light change over fiasco. It was under the kessil, but the right side of it wasn't getting much light as I didn't have a light over the center of the tank. Right side of the coral did the same thing as the bottom of yours is doing.
Edit: Off topic, but I love the colors on your rock.