Ah, yes, “reasons”.
- Jedi use Ilum crystals, which only come in blue and green. Sith use synthetic crystals, which only come in red.
- Jedi sentinels use blue crystals while Jedi consulars use green.
- Kyber crystal colours reflect the affiliation/temperament of their users.
Blah blah blah bullshit.
Aesthetics and symbolism are the only valid reasons for any lightsaber colour.
How is it “bullshit”?
It’s bullshit because all the stuff you quoted is no longer canon anyway (for example, there’s now no such thing as a synthetic crystal in canon), and new bullshit has been made up to replace it (crystal “bleeding”). And none of it matters to the films themselves anyway.