That is interesting, have not heard that before.
There is also this quote in In Making of ROTJ, page 119.
Wednesday, January 6, was a big makeup and costume fitting day. “In a way, the first two films were an elaborate setup for Jedi,” says Hamill. “I think people really sense that this is the final chapter in the story–so far–and not a cliffhanger. It’s the big finish–all stops out, all systems go. My costume reflects that. During Star Wars, I was in a floppy, white rag-doll-type outfit. For Empire, I was in a militaristic-looking khaki costume. Now I wear the black uniform of a trained Jedi Knight. But the question is: What kind of Jedi? A wizard, a religious figure, or just a glutton for punishment?”
“Luke’s outfit went through incredible changes,” says Marquand. “We just worked and worked and worked. George really wanted Luke to wear black.”
“That was completely George,” says [costume designer Aggie Guerard] Rodgers. “He told me, 'That’s what it is–just copy the white one from Star Wars in black.”
“George was a little worried about my costume, that I would come off as a Hitler Youth or something a little too stark,” Hamill adds.
I believe there are other references to this idea, whether it is from Lucas direct or artists/designers.
I think the rationale here was that Lucas wanted Luke in black for dramatic effect and to make the audience question if he will turn or not. At the time it being a Jedi uniform was the justification for why he would choose to wear black. But then when making the prequels, Lucas returned to the idea of the Tatooine robes being more like the Jedi uniform because 1) audiences already identified the look with Obi-Wan, the most easily recognized Jedi in pop culture (a lot like how Gandalf sort of became the template of the ‘wizard’ look), and 2) the lighter, earthy tones of the Jedi robes made them more easily recognizable as the good guys.
Basically, costumes are an easy way to tell audiences who the good guys and bad guys are. For ROTJ he wanted the audience to wonder if Luke would be bad, but for the prequels he wanted the audience to immediately recognize the Jedi as good. In universe, I think the argument for the Tatooine robes is that they are reminiscent to clothes of the impoverished, simply-dressed citizens of the galaxy. And the prequel Jedi harken to the concept mendicant, ascetic monks, and the simple robes play to that idea.