Eye to the right: The deep-sea squid Histioteuthis bonnellii might see with its colour-changing skin David Shale/NaturePL
TWENTY metres underwater, off the coast of north-west Spain, biologist Roger Hanlon is stalking his prey. His camera is trained on a subject that has painted itself beige, grey and white to match the gravelly seabed. It perambulates towards a clump of kelp and, settling itself amid the fronds, quickly deepens its complexion to match their rich red-brown. This colour craft is impressive, but for Hanlon it is also baffling. He knows the common octopus is colour blind.
At least, that is what…
