I like the idea that all pre-RotJ Jedi had blue lightsabers, but all post-RotJ Jedi had green lightsabers. It adds more depth to Return of the Jedi that the new lightsaber color means a new era of Jedi.
I personally like blue for apprentices and Green for masters. So Obiwans saber in ROS and ANH is green in my personal versions. This works with the sequels as the only one with a green saber is master Luke. Ben, Rey and Leia were apprentices and use blue sabers
Edit- This thematically plays into different things too. Like Anakin never became a master (As the council denied him) so he only ever had a blue saber, where as his son Luke shows up with a green saber. Which along with the fact that Luke was even trained should irritate Vader as he was too old to be trained and denied being a master. Luke showing up in Rotj should not just irritate him, it should remind him of what he lost and passed on in his path following Sidious. Along with Luke saying “Im a Jedi like my father before me” are encouragement to his character as a person. That he can still do the right thing and still be a Jedi (even if only at heart).
Luke having Green in the sequels represents the masters and what Snoke, Sidious, and Kylo are trying to destroy. Along with what Rey is trying to become. Reys saber at the end of the Sequels (staff) should have been green. Imo
Edit edit- Though her yellow saber is appropriate too as mixing Green and Red light gives you yellow. So you could go either way their but i would go green and not imply shes imbuing the sith side with her jedi side. Which is why Mace should have green too.
Sorry, so many thoughts on this.
Obiwan’s saber being green in ROS and ANH makes more sense also for Lukes in ROTJ, as it looks just like his. Luke is now a jedi, and using a model similar to his masters. (Also luke is literally using the saber prop of Obi’s from ANH in all the scenes except 2 close up vanity shots)