... not sure of Blue bottles or other jellies, but I watched a Discovery doco on box jelly fish and they see and can distinguish colours. In the doco they tested it by putting a box jelly fish in tank and put two rods in and when rods a black colour, would swim around them, when white, swim right up to them and when red, it would swim into the corner of tank and stay there. They figured, when black its similar to mangroves so swim and manouver around the object, when white its like fish so a bit of food, go get it. When they see red, it must be danger so swim away. Oh, and they can swimm very very fast too. They tracked one and it swam the same speed as a long distance swimmer.
Lucky for us, when its on conditions (wind and waves etc), the box jellies nic off, too rough and would get mashed up so were ok to ride with no stinger suit but if its calm for a few day, watchout!
I reckon the extra jellies in Perth is a result of the warm water pushed down by the cyclone recently (Narelle).
cheers for now,
Robbie