That is true. In the wild, they're naturally green.

They flock in the thousands too, so you would probably just recognize them as a swarm of green in Australia.

From what I've heard though, apparently some pets have escaped and joined wild budgie flocks, so I guess some of these swarms are a little more colorful now.

Same with cockatiels. Pet cockatiels have escaped and mated with wild ones. There are different mutations in the wild now.

So, if youre in australia, can you release pet birds? like even if theyre born in captivity?

No. They wouldn't know how to survive, but some have managed somehow.

If I remember correctly, Australia has some strict conservation laws so I'm pretty sure that would be illegal.