I had my arse plonked on the back steps the other day, while the kids were moving a Praying Mantis from one spot to another, and watching the thing change color. It's pretty amazing stuff.
Of course, one of them then noticed the Keyhole Cichlids on a more recent morning, and how different they looked. I'd seen this before, but watching insects change color on demand sort of brought it to the fore.
These first shots are our breeding pair. You can see the 'keyhole' shape on the side of the body. I don't remember which is male and female. I think the males fins may be longer.
Now, take a gander at the one below. I think it's the one on the left. What they do, is snuggle in next to one of my stumps, which is practically black, under the umbrella of Echinodorus leaves. They also bury themselves in the detritus of dead leaves and Algae, that drifts to that location. I have often missed seeing them, because of this unexpected pigmentation.
I don't know how long it takes, certainly under a couple of hours. Anyone with other Aquarium examples?...
And for a really quick and nasty Biology lesson: Chromotophores are the cells under the scales, that contain Biochromes, the pigment that changes color.