THey use a dye in the water they are grown in.. soft corals which take in water, take in the dye and slowly change colour.. tell tale sign is when a coral comes in and the bag of water it came in is coloured like the coral
The stress causes the coral to release some dye. The dyes usually last weeks if not months..
I have read of stories that Japan is the biggest importer of such corals, and when they loose their colour they are merely discarded and replaced with another one.. this is a sad practice indeed...
I am not sure the marine center is actually selling the dyed coral, but warning that come may be floating on the market. The wording is a alittle confusing..
Mike