Coral Issue?

[viorio]

Can anyone identify what is going on with this coral? It is subtle in the picture, but there seems to be a coralline color/substance beginning to spread.

 

[nautical_nathaniel]

Parts of it appear to have died back, which exposes the original skeleton. Once exposed, it's the same calcium carbonate that makes up the rest of the structure of a natural reef and coralline, algae, other corals, etc. will start growing on it.