How do you tell if a frog is poisonous or not?

My friends and I were in my backyard when my Mom saw a bright green frog. It wasn’t a toad. We thought it might have been a tree frog cause of the body. Though it doesn’t have red eyes and the feet colors too. We want to keep it but we don’t know if it might be poisonous,We put it in my bug catcher and we came back and it changed to dull green with black spots.But the pupils are still brown. Is it poisonous or not?