Why Didn't Anakin's Lightsaber Turn Red When He Killed the Younglings?

Though they have some weaknesses, lightsabers are probably the most iconic part of the Star Wars universe because there is at least one lightsaber fight in every film. They usually indicate a Force user and represent the user's connection to the light or dark sides of the Force. The lightsabers in A New Hope were blue for the Jedi and red for the Sith. That gave fans a quick visual cue that someone was a hero or a villain. For production reasons, Return of the Jedi added green to the list of Jedi lightsaber colors, but red blades for the Sith stayed a hard and fast rule.