Green-coloured lightsabers are generally associated with perhaps a little less orthodox Jedi than blue. The first time green appeared on-screen, it was in Return of the Jedi. It may have been a bit of a shock, and perhaps somewhat intentionally raising doubts in the audience.
To refresh that setup: last time the audience had seen Luke, he had lost his hand (and lightsaber), found out that Vader was his father, and Vader attempted to turn him to the Dark Side. In RotJ, he suddenly returns in a black cloak, acts very confidently, and the first thing he does is to Force choke Jabba’s guards and mind trick his majordomo. Then he procures a lightsaber that is neither blue nor red. One might easily wonder, what kind of sorcery is this?
Green is, of course, a perfectly legitimate Jedi colour. About half of the Jedi in prequels wield it. Still, there is a subtle difference, and the shift towards un-orthodoxy is something that can be noted. The first green colour wielder is Qui-Gon Jinn, who, we know, has problems with the Jedi Council, does not entirely respect the hierarchy and often walks his own path. In Episode II, the main green saber wielder is Anakin, whose conflicts with hierarchy are also daily occurrance at the time.
Unorthodoxy, But Also Deep Contemplation
It does not, however, mean that green is somehow “less good” colour than blue. It simply has a different approach. Green is more contemplative. But carefully and critically examining everything may naturally bring one to question also the traditional norms and decisions of the Council. It may be of note that Anakin’s Padawan, Ahsoka Tano, also wielded green lightsabers. Ahsoka’s path perfectly reflects the intention to do good regardless of what the tradition would expect from her.
However, green can also mean simply more focus on the Force and its mysteries. That is likely the case of another green lightsaber-wielder, Yoda. We can look into one of the classics of Jedi lore, Knights of the Old Republic, where green was the colour of Jedi Consulars. Consulars focus on learning Force powers and tend to solve problems by negotiating. They also try to understand things before they act. This may be the starkest difference between green and blue.
Lawful Good vs Neutral Good
There would be more ways to illustrate the difference between green and blue. For example, one could use the traditional Dungeons and Dragons alignment chart: blue would very much correspond to Lawful Good while green is Neutral Good. Or another comparison: in our world, blue would rather represent institutional religion, while green would gravitate towards individual spirituality, or mystical currents within these religions.
Broadly speaking, the breaking line between blue and green lies between action and contemplation, tradition and spontaneity, with all their pros and cons at every given time. At their best, blue lightsaber wielders can be heroes who defend entire worlds against darkness, who would not yield even to the most terrifying enemy, and who would safeguard the purity of their tradition. At their worst, they can become fanatics who do not yield even a pinch to compromise with those who oppose them, and they do not seek to understand the true nature of the problem, preferring to solve everything with swift and decisive action.
Similarly, at their best, green lightsaber wielders can be deep thinkers; contemplative individuals who are able to both dig deep into their own tradition to bring out forgotten gems. At the same time they are flexible enough to bend the tradition and offer new approaches suitable for the situation at hand. At their worst, they can be disrespectful to all authority, unable to team-work, being too individualistic or too focussed on their contemplation to the point of self-isolation and withdrawing from action.
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