Of the many mysteries in Star Wars: The Force Awakens, the unanswered question of why C-3PO had a red arm really stood out? In the film, the classic droid references his new arm, but an explanation is never attempted. While it was thought an answer would be revealed in one of the next installments, an answer has already been given to solve the mystery.
As io9 reports, the origin story of the clumsy droid’s new arm appears in Star Wars: C-3PO #1, a new canonical comic by James Robinson, Tony Harris, and Joe Caramagna. In the comic it’s revealed C-3PDO wears the new arm after his was ripped off in a droid mission on a dangerous, unidentified planet. He wears the arm in memory of a droid named Omri who sacrificed itself during the resistance mission.
We don’t want to spoil everything, so check out the comic if you want more details on the touching story. It sounds pretty harrowing and not at all what I’d expect from a Threepio story.
So no, C3PO didn’t lose his arm and wear the red one because he lost it in a tense outerspace battle or being the clutz that he is. He wears the arm because he’s showing respect to a fallen comrade. That’s a pretty solid explanation.
As or why he’s replaced the red arm with a golden one by the end of the movie, well, that’s an unanswered question for another day.
[Io9]