I think C-List Fodder and Mauve Shirt are kind of similar but coming from opposite directions, and neither one is "the same but more" of Red Shirt.
C-Listers are characters who were brought in as a lead or a guest spot and never got the traction necessary to make it big, so they just faded into the background. They're technically around, but not important
. So the authors feel free to murder them — they're known characters with names and all, but not important to the overall story of the universe. The audience reaction should be "Oh, hey, yeah, I remember that guy from — OH GOD THEY KILLED HIM!"
By constrast, a Mauve Shirt was created for the purpose of filling in the background. They were never meant to be important, and may have been created just so they could die to show how strong Monster #26 is. But someway or other they managed to become interesting to the audience and, against expectations, achieved some kind of popularity. They may be slated to die anyway (the impact all the stronger for being slightly more foreground) but they have a distinct identity.
And both of those are distinct from Red Shirts, who are just faceless, nameless non-characters who mean nothing to the audience and exist only to be slaughtered.
I think this is supported by the descriptions of the tropes.
So, for example, in the Avengers movie, there's the regular SHIELD agents, which are red shirts (nobody cares if they die), and then there's the Mauve Shirt Coulson, who is in all respects just a regular agent except we know him a little better. Or in Venture Brothers, you have #21 and #24 (who are much more than basic henchmen, but they still wear the suit, follow the Monarch, have numbers for names, and so on).
Compare that to, say, the Scarlet Spider or Stilt-Man, who were intended to be major characters and just didn't work out.
edited 20th Jun '12 2:58:50 PM by Escher