Hi Sandi,
 
A rather unusual problem you have there - a coral that somebody tried
to improve by making it look more like coral? -  but I'd be optimistic
about getting your specimen cleaned up.  Hard corals are made of
essentially the same calcium salts that shells are, and the only
chemicals likely to harm the coral are those that would harm shells,
particularly acids.  Fortunately, almost all of the solvents that
remove paint most effectively are non-acidic. A piece of coral could
safely be soaked in paint thinner or paint remover, kerosene,
turpentine, mineral spirits, or other commercial products of that
type, or in purified solvents such as xylene, toluene,
trichloroethylene, acetone, etc. It's hard to know which solvent
might work best, because you may not know what kind of paint you are
dealing with.  But they all mix readily and safely with one another,
and if one solvent doesn't work well, the coral could just be
transferred directly into another.  Caution - the vapors from some of
these solvents can be harmful if breathed - best used outdoors.  Use a
covered pail.  If you live in a northern area, wait until spring.
Also, a coral head like a brain coral is quite porous, and can absorb
a LOT of solvent.  It may take a week of good ventilation OUTDOORS to
completely dry after soaking.  Hopefully the paint will be removed by
one solvent or another.  If necessary, residual bits could be removed
with a stiff bristle brush.  If you are handling the specimen while
wet with solvent, wear good quality rubber gloves (not thin latex
gloves - some solvents may soften them to the point where they are
worthless).  Once the paint is removed (or in the event that you have
an unpainted coral specimen), good old chlorine bleach (Chlorox) is
the best thing to clean it with, if it needs cleaning.  I'd use it
fairly strong, maybe 1 part Chlorox to 4 or 5 parts water.  This will
help: (1) if it's an old, gray or dirty specimen; (2) if all the coral
polyps have not been removed; or (3) if there is any odor (especially
in massive forms like brain coral) from the remains of worms,
mollusks, etc. that have burrowed into it.  Don't use the bleach
until the solvent has thoroughly evaporated from the specimen (no
solvent odor remaining) because bleach is an aqueous (water-based)
solution, and water won't mix with any of the above solvents (except
acetone).  So, if solvent remains in the coral, it will act as a
barrier to the bleach.  After bleaching, the specimen should be
soaked in several changes of water, for at least 24 hours, to remove
the bleach, then just dried.  If there is a mild odor, don't worry
about it.  Once the specimen is thoroughly dried (which again may
take a week or more), the odor will be gone.  If you intend to place
the coral in an aquarium with fish or other live organisms, it is of
course especially crucial that all traces of solvents and bleach be
thoroughly removed!
 
Paul M.