So, this is the holy grail of sea slugs.  Or one of them.  Search for “Holy Grail Nudibranchs” and you’ll come up with more than a few.  But on Maui I’d say these provide as much of a thrill upon discovery as a Pikachu.  And that’s pretty significant.  They are beautiful.  There are not many green, blue, yellow, and white sea slugs in the Hawaiian Islands and these have the added beauty of fluffy white/translucent angelic lace-like gills and patterns that are totally inconsistent and mesmerizing.  Their rhinophores are usually a beautiful sea green with delicate white spots and their tails have a similar appearance to their rostroms (noses?), leaving one to wonder, at first glance, which way is forward.  These are as rare as they are beautiful, but we spotted a number of them in the winter of 2018/19  in the North Kihei and Maalaea areas of Maui.  All were found in less than 10 feet of water and most were on the move.  To about 2 inches or 50 mm. The juvenile was no bigger than a dime.  For a more serious take, more photos and a discussion of the possible variance in colour check out Sea Slugs of Hawaii.