The Unknown Spectator is the narrator of the Abstract Jester and Geo-Robo story. He unlike the other three characters, does not have a set design, as it gives ambiguity on who the Spectator really is. It's possible that the subject is a Mooner, however that hasn't been confirmed.
The Spectator share a similar to the Mooner, being brought into consciousness by the flash of colors. However, it seems the Spectator was the start of the flash, creating the Kolor Machine through a surge of knowledge imploding the Spectator. He seem to be aware of this anomaly, feeling more like a host. Such the creation of the Kolor Machine brought upon the Abstract Jester and the Geo-Robo, although under different circumstances.