This is the Caribbean version of the Giant Anemone (Condylactis gigantea).  They do come in a multitude of colors--some Giant Anemone have blue tips on the tentacles, as this one does, while some have pink, some have yellow, etc.  Whatever the color, I find the gentle movement of the tentacles in tune with the surge to have an almost hypnotic effect.  Every time I spot one of these I immediately hear the background music to some of the U/W videos I have seen.

Anemones are plentiful on the reefs of Little Cayman, but this is one area where I think the cold waters off California produce a greater abundance and greater variety.