Lightsabers don't automatically turn red when one turns to the dark side. Anakin never bled his kyber crystal in the prequels, explaining why his saber stayed blue. Anakin's lightsaber needed to ...

Addressing lightsaber colors, ‘Star Wars’ creator George Lucas once said, “Good guys are green and blue, bad guys are red” Yuri Gripas ... before clarifying he has “no preference ...