No, not all of them. Before being defeated at Mustafar by Obi-wan, Darth Vader did use his blue lightsaber until Obi-wan took it from him after his defeat and being left for dead. And ancient Sith, like Exar Kun did use a blue double-bladed lightsaber.Moonmover said:If I were a Sith, I would use a red one. Duh. They all use red ones, right?