The character Otho ("Otto" in the German series) is, according to Wikipedia, a green-skinned android. But actually it is never shown that he is a robot.
Does the series or comics show any pictures or stills with a scene, that proves that he is a robot and that he is green?
On this picture from http://www.robertweinberg.net/captainfuture.htm it seems like he is green:
But I am not sure, if that supposed to be Otho.