Now you’ve got me started on lightsaber history!
Only one lightsaber color is mentioned in the 1974 rough draft – that of protagonist Annikin Starkiller – and it’s red.
Ralph McQuarrie’s production paintings for the 1975 second draft introduce the idea of multiple colored lightsabers. But these are still a bit unusual: in his painting of Darth Vader dueling Luke Starkiller’s brother Deak, Vader’s saber is blue and Deak’s is golden. Meanwhile, lightsaber-wielding stormtroopers have white lightsabers to match their white armor.
George Lucas initially tried to achieve the lightsaber effects in-camera by using special spinning rods (powered by hidden electric cables) with a luminescent coating. When a light was shone on them, they would appear to glow. This method only allowed for one color to be used on all lightsaber blades in the same shot. Tests on the Blu-ray show that red and blue were considered, but Lucas ultimately opted for white lightsabers across the board.
A few of Ralph McQuarrie’s later publicity paintings for SW 1977 adopt this design – for instance, his early art for the novelization cover, which is a new version of his painting of the Deak/Vader duel.
When the in-camera effects proved unsatisfactory, Lucas decided to use rotoscoping to enhance the effect. This allowed for McQuarrie-style individually colored blades to be introduced.
Evidently the initial notion was red = good and blue = evil, matching up with the blue saber color McQuarrie gave Vader, as well as Annikin’s lightsaber color in the rough draft. But as we now know, Paul Hirsch convinced Lucas to flip the colors. (As Michael Kaminski has also noted, the 1977 film’s lightsaber color scheme matches the color motifs of swords in Lord of the Rings.)