I've heard that theory, too, and maybe there is something to it; but most of their potential predators are also color-blind or nocturnal invertebrates who hunt primarily by chemical sensors. I still can't help but suspect there is something else going on, some kind of adaptational over-response. I'm no creationist, but I still can't shake the nagging suspicion that there is more to evolution than we know, that there is something else going on we still haven't quite figured out.

I've always been fascinated by these little guys, they are delightful. There used to be a web site that had a "sea slug of the day" picture every day, and they were always visually stunning.