Even at a pretty young age, though, it always amused me that some of easiest animals to find were the supposed masters of camouflage - the chameleons.
Even if you aren't that into lizards - which I'm willing to assume that you aren't, seeing as the vast majority of the world is - you've probably heard of chameleons. If you can't tell a gecko from a varanid from an iguana, you'll never mistake a chameleon for any other lizard. With their curling tails, pincer-hands, and crazy eyes, each on its own turret and capable of independent movement, the 200-odd species of chameleon stand out as species - and that's also without taking into account that yo-yo of a tongue, capable of snatching up insects... or small birds from a distance. Oh, and if that wasn't weird enough, many species have horns, making them look like little dragons.
(Confession: I once had an asshole - hilarious, mind you, but still asshole - of a boss who convinced me that, if I put crickets between my lips, our panther chameleons would tongue-zap them out from my lips, thereby dazzling crowds of zoo visitors and making me some sort of zoo celebrity. Instead, I stood for ten minutes with a bug in my mouth, while chameleons and guests alike looked at me like I wasn't playing with a full deck. I later found out he did this to all new keepers. Well played, sir. Well played.)
Of course, if chameleons are famous for anything, it's their color. Unfortunately, this is one of the those times when pop culture has gone on to make an animal's adaptation an exaggerated parody of what they really are. No, you can't put a chameleon on a checkerboard and watch it instantly turn into red and black squares. They're camouflaged, not invisible.
As it turns out, however, camouflage is only a small part of why chameleons change their color. Typically, they do it to convey their status and emotions; think of them as scaly mood-rings. They use their coloration to impress mates and intimidate rivals. Brighter colors are for showing up. Darker colors are signs of submission. It also has the ability to help them absorb more sunlight (many lizards can lighten or darken themselves to soak up the sun, usually in a more subdued fashion).
I'd love to explain the exact mechanism which allows a chameleon to change color, but I'm not very good at it. My expertise with animals ends at the cellular level, and when I start to read about nanocrystals and pigment-organelles, I have a regrettable tendency to go blank. That being said, not understanding how something happens doesn't make it any less remarkable that it does.
Chameleons aren't as well represented in zoo and aquarium collections as many other groups of lizards. They tend to be somewhat delicate in terms of their temperature, humidity, and ventilation requirements. They also get stressed easily, and males especially have to be kept visually segregated. Most zoos that display chameleons keep a member of a small handful of species which are especially hardy - the veiled chameleon of the Middle East, for example, or Madagascar's panther chameleon. Madagascar, incidentally, is the hub of chameleon diversity, with a whopping half or so of the world's species found there.
Visitors to a zoo reptile house are unlikely to be treated to a light show of rapidly changing colors. An undisturbed chameleon is apt to stay its basic, background color. The lucky guest may be treated to the sight of a chameleon climbing in the branches, its unusual, jerky walk mimicking a leaf trembling in the breeze. The very lucky guest may even see a chameleon hunting, stalking its prey, sizing it up, and then seizing it with a harpoon-like tongue.
If you see some dumb keeper with a still twitching cricket held between his or her lips, you'll know my old boss has gotten himself a new hire.