Lucas originally planned to make Luke’s lightsaber red and Vader’s blue, but Hirsch suggested switching them because of his knowledge of Christian iconography from the Renaissance era he’d studied in art history at Columbia University in the mid-‘60s.
from this article on Paul Hirsch’s new book
This dovetails with mention of the early lightsaber colors being swapped (and the tractor beam gauge also) in Paul Duncan’s SW Archives book.
I have given a name to my pain, and it is Paul Hirsch.
*shoots laptop*