|MadSci Network: Zoology|
Wow what an excellent question!!
Octopi have one of the most complex eyes in the animal kingdom, and it's with these eyes that they can judge their surroundings and see just what colour they need to be!
Some octopi change colour depending on what mood they're in too. Scientists haven't figured out which colours mean what though, but there is an octopus here in Australia (where I live) called the Blue Ringed octopus and when it's cranky it has bright blue rings all over it's body.
I found this great web page for you to have a look at... http://www.marinelab.sarasota.fl.us/OCTOPI.HTM
It's full of interesting information and links to other sites about the octopus.
Have fun learning!!
Try the links in the MadSci Library for more information on Zoology.