These are simple, but I needed more alien types quickly so made these quick textures if anyone else can use them.
https://www.dropbox.com/s/easleqj5vygte3n/alien_blue.png?dl=0
https://www.dropbox.com/s/kxfa4v99t4al9ee/alien_orange.png?dl=0
https://www.dropbox.com/s/0rw40520f8zhl4u/alien_purple.png?dl=0
https://www.dropbox.com/s/f3jvy1nqbhf4dq4/alien_red.png?dl=0