In essence, a lightsaber’s color reveals something about its wielder and their personality. Lucasfilm’s Pablo Hidalgo has explained that the Kyber crystals used to make lightsabers start out colorless. The crystals only take on a color once they have been gathered and a bond between the crystal and the saber’s user has been formed during the creation of the weapon. There’s even been an instance in which a yellow saber was made from unstable red saber crystal, when Jedi Jaden Korr purified it and the crystal turned yellow, granting him his third lightsaber.
Just like the blue and green lightsabers, the yellow lightsaber is associated with an important school of thought within the Jedi Order: that of the Sentinels (via Ultra Sabers). Star Wars lore explains that the Sentinels seek a balance between the Consulars and the Guardians, and also wish to educate themselves on other more practical aspects of life such as tracking techniques and espionage. Unlike some others in the Jedi Order, Sentinels recognize that the Force isn’t actually the solution to everything.
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