Obvious spoilers follow for Star Wars: The Force Awakens.
We know that C-3PO has a new red arm in Star Wars: The Force Awakens, but that's about all we know. Then at the end of the movie, C-3PO has his regular golden arm back (or a new one).
So what gives?
Well, pieces of the puzzle come together (albeit not competely) via the following image (guessing from the Force Awakens Art book) which offers that C-3PO "is uncharateristically quiet when it comes to discussing his salvaged arm; it is a memento of another droid's sacrifice."
Interstingly enough, the end scene when C-3PO has his regular arm back also features another droid --Â a red protocol droid to the right. We can probably speculate that since R2 went comatose, C-3PO may have parterned with another droid.
No worries though, as Marvel Comics has us covered. February 24th sees Marvel put out the Star Wars: C-3PO one shot comic book explaining the red arm. Here is the description:
â€¢Â Follow everyone's favorite protocol droid as he Journeys to Star Wars: The Force Awakens, in this special one-shot leading up to his appearance in the film! Just how did Threepio get a red arm, anyway? Find out here as the blockbuster creative team of James Robinson and Tony Harris of DC's Starman reunite for the first time in nearly two decades!
â€¢Â Â You may be fluent in over six million forms of communication...but this book is a must have in any language! Â
Pic (via reddit) and comic cover below: