Roy is a much better person to ask that question. He spends much more time watching them in tanks than I do and he's been keeping them for ages. Almost all of my experience keeping pygmies in tanks has involved helping him with animals in his lab- generally trying herd the animals around to help him get some of those great photos. Other than that I've kept a few temporarily in the field. I like one from Moorea but it does not travel well or seem to do well in closed seawater systems. In general I like all octopuses for differrent reasons so I don't have a favorite. When thinking of species for the aquarium I think as much about collection techniques (i.e. the possibility that Indo-Pacific pygmies could be caught with cyanide) as I do about personalities. Roy really likes O. wolfi and I agree they're an interesting looking animal. Plus we have a lot to learn about them so they're exciting in that respect, but that doesn't necessarily make them a good pet.
I'd like to see someone breed O. digueti. We had one in lab and it was pretty exciting. They're one of the few octopuses that court during mating (Janet Voight's work in aquaria), and they lay large eggs. Cool behavior, cool-looking animal, small- and it can be cultured!
I don't know that all octo species have been studied, but in general that's the belief.
However, not all red light is monochromatically red-- a lot of the time, even if it looks red to us, it includes other colors as well. Usually LED red light is truely just red, but any sort of incandescent or flourescent light will have other colors, and if it's filtered with a red filter, that will probably let through some light that the octo can see, even though it seems insignificant to human eyes because there's so much more red. In particular if it's got some yellow/orange, it could be in the octo's range, and if it's at all pink, the white part of the light will go well into the octo's visual range.
This is starting to be a very frequently asked question, so I just spent a few hours looking up papers... I think I'll write up a mini-article on this. Unfortunately, though, I haven't found a reference yet that describes the width of the spectral response for cephalopod rhodopsins, just the peak positions.
This means that an octopus can't see light frequency that's "redder"
than yellow-orange, but can see blues and greens just fine, probably
better than humans.
Note that although firefly squids are known to have 3 visual pigments,
and therefore color vision more like humans than the monochromatic
vision of most cephs, all three pigments are still in the blue-green
range: 470nm, 484nm, and 500nm. (Note, though, that the 484nm pigment
and the other two are located in different areas of the retina,
however) See http://www.springerlink.com/link.asp?id=p21210724627v321
most cephs can also see polarization of light, which humans
cannot. Some may also be able to see a bit into the UV range.
Nope, but I was figuring on going to the library and xeroxing all the pre-internet stuff like that... thanks.
I actually just ordered the (very expensive) JZ Young and Marion Nixon's "The Brains and Lives of Cephalopods" and the Hanlon/Messenger "Cephalopod Behavior" books, since I just got paid so I'm giving myself a treat...