In Star Wars: The Force Awakens, we run into our old friend C-3PO:
Goodness! Han Solo! It is I, SeeThreepio!
You probably don't recognize me because of the red arm.
Look who it is! Did you see who? Oh. Excuse me, Prin-- uh, General. Sorry. Come along, BB-8. Quickly. (BB-8 beeps)
Yes, I must get my proper arm reinstalled.
For some reason, he has a red left arm. However, the situation/reasons behind how he got this red arm is glossed over.
Is it just a fresh coat of paint on his old arm? A salvaged part from another (presumably destroyed) Protocol droid? A newly manufactured arm that is able to perform more/different functions?
Answer
This was revealed in Star Wars Special: C-3PO #1
He loses the arm to a sea creature, which rips his arm off.
The droid OMRI (whose coloring/paint-job is black) is destroyed by acid rain. The acid rain strips the coating of black paint from OMRI’s metal casing as well revealing the original red coloring casing beneath the paint. C3PO takes OMRI’s arm with him to replace his own lost arm. 
Source: ComicBookResources

Comments
Post a Comment