American actor Mark Hamill on the set of Star Wars: Episode VI - Return of the Jedi
Movies - TV
Why Star Wars Changed Luke Skywalker’s Lightsaber From Blue
To Green
While “Star Wars” lore has offered answers as to why Luke’s lightsaber changed from blue to green, the real reason has more to do with visual effects than story.
Promotional art for “Return of the Jedi” featured Luke with his blue lightsaber, but it was changed to green in the final product to contrast with the blue sky of Tatooine.
Executive creative Pablo Hidalgo stated, "As much as we like to mythologize why it's green [...] sometimes there are very pragmatic filmmaking reasons behind these things."
Of course, Luke had lost his blue lightsaber at the end of “The Empire Strikes Back,” so it was ultimately a switch that worked well in-story too.