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human
[Star Wars] What is the reason for there to be very few users of purple and yellow lightsabers or lightsabers of other colors?

Is there any explanation in both Canon and/or Legends? In Canon we only have Mace Windu with a purple lightsaber, and Rey Skywalker and the Temple Guards with yellow lightsabers (and Cal Kestis if you choose him to have one in Fallen Order). In Legends Darth Revan and the Dark Woman both had purple sabers, but I think that was it, and Bastila Shan had yellow lightsabers.

As for other colors, Ahsoka Tano is the only one we know with white lightsabers, and Cal Kestis can also have white and orange lightsabers in Fallen Order. Why are these different colors other than blue, green and red so rare if there's countless of crystals of all colors? In Canon I think at least it could be suggested that it's harder for a purple, yellow, orange and white crystal choose its wearer, but in Legends, where colors were merely chosen by its user, it's even weirder that we rarely saw other colors.
gpt
Lightsaber colors are essentially meaningless in Legends (crystals are naturally found already colored). There's only one scene in Knights of the Old Republic that attempted to give them some semblance if meaning, but it's a holdover from the pencil&paper RPG that the game uses for its ruleset - and the colors can be switched out immediately to any other you have in inventory.

In canon, lightsaber colors only have some vague, not really understood link to mindset, with the exclusion of red and white - the former being a dark sider "bleeding" a crystal (forcing it into submission) and the latter being a bled crystal that's been healed by a light-side Force user.