At this point in the Star Wars universe, lightsabers come in every color of the rainbow, but that wasn't always the case. Once upon a time, heroes had blue lightsabers and villains had red. So what exactly was the deal with Luke's green lightsaber? For years fans have wondered if there was a deeper meaning to lightsaber colors, was the weapon a reflection of its wielder in some way. As it turns out, no, not really. Apparently, Luke's new lightsaber that he used in Star Wars: The Return of the Jedi was originally going to be blue, but it was discovered that it didn't stand out enough against the blue sky and yellow sand in the rescue of Han Solo from Tatooine, so the color was changed to green. As Lucasfilm story team member Pablo Hidalgo says, the change had no meaning beyond filmmaking necessity. According to him...
The intent was the lightsaber was going to be blue. In that universe, at that time, as far as anyone knew, lightsabers were red or they were blue. As much as we like to mythologize why it's green and what that all signifies, sometimes there are very pragmatic filmmaking reasons behind these things.
Since the introduction of the green lightsaber and the purple one used by Mace Windu in the prequel trilogy, there has been some indication, though mostly in the now non-canonical expanded universe, that the kyber crystals that are used in lightsabers can be modified in particular ways in order to produce different colors. Since the user has to choose to make these changes, there is at least a passive relationship between the color and the Jedi. However, as Pablo Hidalgo explains to Vanity Fair, none of that was part of the original intention of giving Luke the first green lightsaber, it was an entirely a filmmaking decision.
Pablo Hidalgo is asked in the VF piece about Luke's old green lightsaber and whether we'll see it again in Star Wars: The Last Jedi. As one might expect, he's not clear in an answer. Rumors have indicated that Luke does still have the weapon he constructed and that he will wield it in the film. In the meantime, the weapon that once belonged to Luke's father, the classic blue saber, will continue to be wielded by Rey as she begins her training under Luke, as we've seen in the film's first trailer.
With a limited number of Force users and available lightsabers, we probably won't be seeing any new or interesting colors in the current trilogy. Still, it's good to know that this is one mystery we don't need to worry about. There are so many others we need to focus on.