ULethbridge Scientist Studies How Octopuses Do It

I am personally surprised that this has not been studied in depth by Japanese scientists (and if you don't understand why I suggest you don't try. Seriously).

Male common octopuses (Octopus Vulgaris), for instance, are known to rear up and display several large suckers on the underside of their tentacles to identify themselves as male, but only if approaching a larger female, which may decide to attack and eat them. They will also spread themselves out to appear large, and turn a dark or pale coloration.

A male day octopus (O. Cyanea), on the other hand, will stand tall and tower over his potential mate, while turning pale — as he approaches a female, he’ll flash a distinctive pattern of black stripes across his body.