On a nature documentary whose name I don't recall [1], they showed a great example of a cuttlefish disguising himself.

There was a larger than average male with a harem of females, and there was a smaller than average male that wanted to mate with the females, but was nowhere near strong enough to beat the big male in combat.

So the small male took advantage of his small size. He took on the appearance of a female, and approached the large male as a female would.

The large male was fooled, and accepted the small male into the harem. As the large male continued vigilantly watching for approaching challengers, the little male mated with all the harem females right under the big male.

[1] I almost certainly saw it on one of the Nat Geo channels, one of the Discovery channels, BBC America, or PBS.

Edit: a bit of Googling turned it up. It was in the BBC documentary series "Life" from 2009. It's this segment: http://www.bbc.co.uk/programmes/p005bpsl

I misremembered a little. The large male only had one female, not a harem, when the small male joined.