Q&A's About 'Star Wars': If Luke Skywalker’s lightsaber was green, how did it turn blue in Star Wars: The Force Awakens?

In the classic Hildenbrandt Bros. Star Wars poster, Luke's lightsaber is yellow. © 20th Century Fox Film Corp. 

In Quora, Sam Lee asks:

If Luke Skywalker’s lightsaber was green, how did it turn blue in Star Wars: The Force Awakens?

My reply:

It seems, my friend, that you need a little refresher course in Star Wars History 101.

Recall, please, that Luke Skywalker used two lightsabers as a young Jedi-to-be in the Original Star Wars Trilogy (Star Wars, The Empire Strikes Back, and Return of the Jedi.

The first lightsaber Luke possessed was originally his father Anakin’s; it was retrieved from the ashy ground of Mustafar by Obi-Wan Kenobi after his fateful first duel with the newly minted “Darth Vader,” the Sith identity Skywalker pere adopted when he was seduced by the Dark Side of the Force. Obi-Wan kept his former Padawan’s “laser sword” hidden away for 19 years during his exile on Tatooine, waiting till Fate - or the Force - reunited “Ben” Kenobi with Luke in A New Hope (the original Star Wars from 1977).

As you can clearly see, the blade of this lightsaber is blue-white.

Now, despite the iconic poster art that depicts Luke brandishing his lightsaber defiantly in a heroic over-the-head grip, in Star Wars (aka A New Hope), the young farm boy from Tatooine only uses it one more time in the first movie - during a brief training session with Ben aboard the Alderaan-bound Millennium Falcon:

Luke will keep this lightsaber over the next three years, although without a Jedi Master on hand to train him, it’s doubtful that he uses it much while he is serving the Rebel Alliance as an X-wing fighter pilot. (I mean, he probably uses it on occasion in untold stories set in the time-jump between A New Hope and The Empire Strikes Back, but he’s clearly not an autodidact Jedi Knight.)

The next time we see Luke wielding his father’s lightsaber after that brief sequence on the Millennium Falcon is when he uses it to escape from the Wampa’s cave on Hoth:

In the last third of The Empire Strikes Back….that’s when Luke uses his lightsaber for the first time against another lightsaber-armed Force user…Darth Vader. In a protracted duel in Bespin’s Cloud City, the not-fully-trained Jedi faces off against Vader during an ill-advised attempt to rescue Han Solo and Princess Leia from the Empire.

Luke manages to hold his own a couple of times during the early phases of this clash of lightsabers until this happens:

As you can see, throughout much of the Original Trilogy, Luke’s lightsaber - Anakin Skywalker’s - emits a blue-white blade. At least, it does so until it is lost (along with Luke’s right hand) in the reactor control room in Cloud City).

Because circumstances prevent Luke from retrieving either his hand or his father’s lightsaber at the end of The Empire Strikes Back (Cloud City is under Imperial occupation, TIE fighters have chased the Millennium Falcon into space in an attempt to drive the ship (and its fleeing Rebel crew) toward the waiting Executor, and Luke is in no shape to do so even under the best of circumstances), everyone assumes Luke is now disarmed - literally and figuratively.

So, in the one-year time jump between Empire and Return of the Jedi, Luke returns to Tatooine, goes to Obi-Wan’s abandoned home and finds the old Jedi’s books, tools, and even parts for a new lightsaber.

As you can see, my young apprentice, the lightsaber blade in Luke’s new saber is no longer blue; it was going to be, but tests showed that the blue-white blade would not show up properly against the blue sky in the Sail Barge assault scene, so Lucas had to improvise and told the effects crew to make the blade green instead.

So it came to be that when Luke finally confronted Darth Vader on Death Star II near Endor, he fought the final duel against his father with the green-bladed lightsaber:

Many years later, Luke’s original lightsaber, the last one built by Anakin as a Jedi, was found and somehow fell into the possession of Maz Kanata, a space pirate and a friend of Han Solo’s.

It is at Maz’s castle that Rey, a Force-sensitive scavenger from Jakku, finds the Skywalker Saber with the blue blade:

Luke Skywalker, incidentally, never loses his green-bladed saber; or if he did in the 30-year time gap between Return of the Jedi and The Force Awakens, we are never told.

But the green lightsaber never changed its blade color to blue; the two lightsabers are different, even though they were both once Luke’s.