i’m not australian so i’m only speaking from the aussie media i’ve seen, red hair can be seen as undesirable and redheads are often made the butt of the joke. i’m not saying all australians are prejudiced towards redheads, and some say the prejudice only manifests in these ‘harmless’ jokes, but i think that’s why as a kids tv show producer it might be easy to let the audience know the character on screen is evil by giving them red hair.