Okay. Luke has the SAME saber in ANH and ESB. Ben had his OWN saber in ANH, which was lost upon his death. In ESB, when Luke's hand was lopped off, he lost his [father's] saber, thus requiring him to build a NEW one in ROTJ, which was originally meant to be blue since blue = good and red = evil for ANH+ESB. But the blue did not stand out well against the blue sky on Tattooine, so, since it was an all-new lightsaber anyway, Lucas decided to change it from blue to green.

There. Why were we arguing about that again?