Are you referring to the very bottom portion of the coral, from the pic looks about the lowest half inch where it attaches to the rock?
If so, that's not brown, that's just dead. The tissue has receded up from the base. Is the coral growing at the tips? It's possible for it to recover, but tissue recession like that is usually caused by something that irritates the coral near where it attaches to the rock, which could be a) not enough light, though IME the tissue just gets really dark and doesn't recede like that for that reason alone b) something on the rock is annoying to coral. Certain kinds of algae can do that as well if they grow around the base. Aiptasia can do that to a coral as well.
Generally if the coral is in good health it should recover assuming you can isolate what is causing the tissue recession and remedy it.
What are you parameters?
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