A lightsaber’s color could be based on how often it is used, with the crystal wearing down and displaying ever redder colors over time:
(I imagine that the purple part of the spectrum would be a bright, almost white pink with the blade gradually shifting blue)
This would make sense of why building a lightsaber is a rite of passage for every Jedi Knight instead of simply inheriting ones from previous generations, while also allowing for a test of skill if they wished to merely replace the crystal in an older saber. The reason Sith blades are red could be for many reasons, such as a reliance on violence and also a disinterest in the serene delicate work required to replace the crystals.