Back when Star Wars was good this was the reason:redline248 said:
Very well could be. Someone who out nerds me in Star Wars lore will have to chime in on the red blade, though.
"However, the defining feature of Sith lightsabers was the use of synthetic crystals, as opposed to the Adegan and Ilum crystals favored by the Jedi. Almost all synthetic crystals used by the Sith featured a red coloration, as a result of the forging process used to create them, though adjustments to this process and manipulations through the Force did result in crystals of different colors."