This is a questionable identification, as are so many, but the closest I can come to a similar flatworm is one photographed and described by Cory Pittman on John Hoover’s Flatworm site.  At first I thought this was a variation on a  Stella’s Flatworm (Pseudobiceros-stellae) due to its dark background and white spots, but this one clearly has a blackish/blue margin and a lighter body with pseudo tentacles that match a Psedoceros species more accurately.  Found in Makena area of South Maui. 20-25 mm in less than 2 meters of water.