Most flasher wrasses stay small and are pretty laid back. (The exception might be the eight-line flasher from the Red Sea. He's got a reputation as a cranky guy - for a flasher.) They'll cruise about above the coral, picking plankton, and occasionally ... flashing. During nuptial displays, the males' fins are at full extension, and colors can take on an otherworldly beauty and glow . . . for a few seconds, then it's all over. 'Til next time. Their colors are variations on a theme, the theme being red-orange, with stripes. Some are redder, with less striping (linespot, blue), some are yellower, with clearly marked stripes (filamented, Carpenter's, McCosker's). Some have one filament on their dorsal fins, some have many, some have none at all, but pack sail-like fins, instead.
Fairy wrasses come in a much wider array of colors, sizes and temperaments, from the smaller, generally peaceful Lubbock's wrasse to the Scott's fairy, at about 7" and packed with attitude. Some hold their colors well in aquariums, others ... not so much. I've got a Laboute's fairy in my tank - beautiful fish, decked in maroon and yellow striping, with blue accents and a pale purple wash across his belly ... until he got under my reef lighting. All of those beautiful colors and patterns have been painted over by a dramatic wash of carbon black. yay. woohoo.
Both groups tend to be relatively easy to acclimate, hardy and disease resistant - compared to angels and tangs, anyway. Both groups sleep in a mucous cocoon in the rockwork, and care not a whit about sand. Fins run the gamut - from rounded and rhomboid tails, to double-emarginate and lunate to pintails. One has a filamented dorsal, but he's also got a reputation as a cranky lad.
~Bruce