Most of the characters in the background, like in crowd scenes, if they don’t have a speaking part, chances are they’re colored basically purple and blue. We experimented a lot with the color on this show--at least Glen did, and that was an idea he came up with to really put a visual focus on the characters that we want to focus on. We figured all the background characters we would color them pretty much monochromatically.
--from the commentary track on "Rebirth, Part 1."