The Sith Lords have an ancient process that explains why all their lightsabers are red in the Star Wars galaxy. While Jedi Knights have several different lightsaber colors with blue and green being the predominant crystals most often seen, the Sith's crystals are all red. There's a very dark reason for this, one that has been developed across multiple mediums beyond the canon movies and shows.
Beginning with Charles Soule's Darth Vader comics series in 2017, the origins of red kyber crystals were revealed with the confirmation that they aren't found naturally in the galaxy compared to those used by the Jedi Order. Instead, a red kyber crystal must be forged using an incredibly dark tradition. Here's how the Sith Lords turn their lightsaber crystals red in the Star Wars continuity.
