Lions live in open dry grass lands so that their golden-brown fur blends in and can’t be seen very well which helps them to hunt.
Chameleons change colour not to blend in but if their scared or hot/cold. It takes a chameleon a few seconds to change colour.
An Arctic fox takes several weeks to change colour between white and brown. It takes the eyed flounder between 2 to 8 seconds to change colour.
Not all animals change colour to camouflage some like the dresser crab collect little objects to wear that will disguise them or some like the tiger just blend in to their surroundings naturally.
Alligators swim with their heads above the water so they can hunt while they swim but when a predator comes they suck their eyes back in to their skulls so that they look like a log.