Irken skin is hairless and green, with some slight variation in its shade from individual to individual, like Humans; for example, the skin color of both Tallests is ever so slightly lighter than Zim's, whereas Tak's is exceptionally pale in comparison. Their eyes have no whites or pupils (much like "Grey" aliens, which are the classic sci-fi aliens), and are only one color; ruby is the most common, but other colors such as various shades of red, pink, purple, green, blue and even yellowish-brown exist as well. It was also mentioned in "Walk of Doom" that Irken Invaders have surgically-installed ocular implants - since the eyes Zim was born with are not visibly different from subsequent appearances, it can be assumed that these implants are subcutaneous.