All lightsabers were originally white because they tried to make them as in-camera effects, using highly reflective tape on rotating rods! They abandoned it when they realized the effect wasn’t very satisfying and because the rotating rods would often break.
Well, yes, but I meant in the early scripts. I know the comic adaptation of the first draft made all the lightsabers red, but I don’t know if that’s based on the script or not. I figured MaQuarrie made them white as they by the time of the second draft had probably started to discuss how the effect would be made, and white was the easiest solution (due to the reflective tape, etc. that you mentioned.)