So, why did Luke use the blue lightsaber instead of his green lightsaber? While it's made clear in The Last Jedi that they were pulled from the Millennium Falcon, initially the dice were to play a much bigger role in the Star Wars franchise.
In an interview with Variety, John Williams spoke about his long history as a composer and his desire to do the score for Star Wars: Episode IX.
Explaining that Luke "is basically tailoring this projection to have maximum effect on Kylo", Johnson went on to describe why blue makes for a stronger, more direct emotional appeal to the sensibilities of Kylo Ren - the Darth Vader-obsessed grandson of Anakin Skywalker.
We see the Force perform acts of telekinesis but it also allows for mental manipulation.
Though I admittedly thought that the only theme I liked from Force Awakens was March of the Resistance, I've recently discovered that there is actually a very clever way in which Williams wrote Rey's theme. The truth is, we see the lightsaber split in half - Kylo sees a blinding flash of light and is knocked unconscious, and then Rey takes the lightsaber away before he wakes up.
Of course Kylo Ren isn't confused by the presence of his grandfather's lightsaber.
Since the film's debut, viewers have targeted their hatred towards writer/director Rian Johnson, demanding he be removed from a leadership position in regards to an upcoming trilogy of Star Wars films, in addition to petitions surfacing across the internet in hopes of these audiences having their perspectives heard. "So if you really want to dig into it and get an explanation, you can say that he doesn't 100 percent know what happened to the lightsaber". This will probably be explored over the next couple of years as Star Wars 9 nears completion. They make you feel like family, they were so welcoming, so accommodating and so friendly. We certainly can't accuse him of making lazy mistakes at this point.