Chameleons can change color to match the color of their surroundings. If a chameleon was born
unable to change color, why would it be unlikely to pass on this trait?

Chameleons ability to change and adopt the background color of their environment helps protect and makes them very less vulnerable. Hence, as a result of increased vulnerability to predators, chameleons who are unable to change would likely not survive for long.

Hence, it would be unable to pass on the trait due to low chance of survival.

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Since chameleons evolved to be able to change colour in order to camouflage themselves and avoid being eaten by predators, a chameleon unable to change colours would not survive very long. Because it would be easier to hunt and kill, it most likely will not live long enough to mate and pass on its genes.