 The series features " sky flowers " as a main setting material . They first appeared in the pilot and have since become a common feature throughout the series . When series background designer Kenny Pittenger was asked what they were , he answered , " They function as clouds in a way , but since the show takes place underwater , they aren 't really clouds " . Since the series was influenced by tiki , the background painters have to use a lot of pattern . Pittenger said that the sky flowers were meant to " evoke the look of a flower @-@ print Hawaiian shirt " . 
