It's a building code thing, which can vary at the state or even municipal level.
Generally speaking, more recent rules specify green, since it's easier to see in the dark and doesn't have connotations with prohibited things like red does. There's also now an international standard exit sign that a) is green, and b) doesn't use any text at all, just a stick figure running toward a door.
Could have been any number of reasons. My first guess is that the green ones were just newer. Also, they might have deliberately put red ones in the darkened theater rooms so they wouldn't stand out as much.
You are the end result of a “would you push the button” prompt where the prompt was “you have unlimited godlike powers but you appear to all and sundry to be an impetuous child” – Zero, 2022
I've seen green exit signs in Ohio, but they're few and far between. The red ones are by far the most common.
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Edit: just realized this meant for buildings and not roads
Kentucky seems to use red ones pretty much exclusively, though I'll have to look again when I go back.