Far as I’m concerned, lightsaber colours should reflect the preferences/psyches of their creators. A Jedi head-over-heels in love would have a red lightsaber, an emotionally cold and aloof Sith would have blue, some guys just want to go with their favourite colours, etc, etc. If the prequel-era Jedi Order is a clique of groupthinking cultists, they’d have a limited range of colours/hues — almost exclusively blue. But Luke’s green lightsaber should be a signifier of his individuality and departure from the dogmatism of the old Order, and the various & sundry lightsaber colours of his students would indicate likewise.