Anakin's lightsaber needed to stay blue for continuity. Anakin Skywalker's lightsaber stayed blue throughout the Star Wars prequel trilogy even after he'd fallen to the dark side for one key ...

Obi-Wan Kenobi and Anakin ... Obi-Wan as Luke Skywalker watches in horror from afar. This last battle between Obi-Wan and Darth Vader is known for being much slower than other lightsaber duels ...