The green goblin just likes green There is nothing canonically that makes the green goblins powers have anything to do with green. He just picked green as his motif and stuck with it. Like Spider-Man is a spider man because a spider bit him. He just like
My first defeat as a superheroine and I woke to found myself strapped to this machine, it keeps teasing and making me come over and over again... I hope I still have a mind left by the time I'm rescued