Oooh! In Episode 4, Obiwan says to Luke "This was your father's lightsaber" and gives him a BLUE lightsaber. So, during the duel, I'm assuming that Anakin dropped his lightsaber on the ground before he fell in the lava and Obiwan picked it up. So, when Anakin is back as Darth Vader, equipped with breathing mask and all, he probably reconstructed a new lightsaber which represents his evil (red).
That is why Lucas probably gave Anakin a blue-colored lightsaber for this duel with Obiwan, so it would fit in with the rest of the story. =]
Pumpkins are the only living organisms with triangle eyes.