Incidentally, in the 1974 rough draft Annikin Starkiller apparently has black hair, and Princess Leia is a redhead. In the Dune series Paul Atreides has black hair, and his girlfriend Chani has red hair, which she passes on to their twin children.
On the other hand, the Ralph McQuarrie drawings of Luke and Leia from the third draft, where they're both blondes, are more reminiscent of the original 1936 Flash Gordon serial.
In his first screen outing Flash kept his blond hair from the comics page, but his normally brunette girlfriend Dale Arden was transformed into a blonde herself, in an attempt to capitalize on the popularity of Jean Harlow. (Dale regained her usual dark hair in the later Flash Gordon serials.)
Jean Harlow herself frequently dressed all in white, like Leia in SW.
As well, with the third draft's Han Solo having the brown hair of Buck Rogers, a blonde Princess Leia would also bear a resemblance to the yellow-haired Wilma Deering of the Buck Rogers comic strip.
Han's rough-draft counterpart, Clieg Whitsun, is blond like Flash Gordon. Since Lucas likely already intended to suggest a love triangle here, the relationship between Clieg and the rough draft's Princess Leia would be visually analogous to that of Flash Gordon and the red-headed Princess Aura, daughter of Ming the Merciless. Of course, much like Flash and Aura, Clieg and Leia aren't meant to end up together.