Monroville
It is not so much the "flashback" stuff I would include or comment on, but the end fight between Luke and Vader (4:33 to 5:08). Whether Luke's eyes go "Sith" (at least until the Emperor confronts him and he regains his composure) or not, SOMETHING has to be done to explain Luke being able to overpower Vader. Hell, it also looks like David Prowse just LETS Luke womp on him!

The angry look on Luke's face, the passionate fury he fights with, the scary dramatic music, the constant imploring for him to 'give in to his feelings' doesn't let you understand what's going on, but getting goofy yellow eyes will?

(and nitpit, David Prowse doesnt do that fight :) )