This answer showed me something I didn't know; that Luke's lightsaber was blue in the first trailer for Return of the Jedi.
As we know, Luke used a green lightsaber in the film. That same answer mentions it was to make the blade stand out better against Tattooine's blue sky, but doesn't back it up with references.
Why was the blue blade changed to green?
Of course, Luke lost his old blue lightsaber when he was disarmed by Darth Vader in The Empire Strikes Back. But that was before Return of the Jedi started production. Yet in the trailer for Return of the Jedi, we see Luke with a blue blade, not with the green blade he would use in the final version of the film.
So possibly, the original idea was for Luke to have somehow recovered his old blue lightsaber, or perhaps his newly constructed lightsaber would've been blue like the old one. But at some point between the release of the trailer and the actual film, the colour of the blade was changed from blue to green.