RPF PREMIUM MEMBER
Can you quote a source for the test fit conversation you're referencing? I watched the video posted and it sure sounded like George saying that the black was more Jedi like.Oh that's so cool. I love concept art! Obi-Wan has such a high fantasy look about him. Like he'd fit right in with Jackson's LOTR films.
Going back to Luke in black. Mark had a disagreement with George with how Luke was being written. And as I understand it, it started when Mark was having his costume fit. Mark noticed that he was wearing black, and had a glove, and a dark cloak. So he asked George what was up. And apparently George told him, that it was meant to show that Luke was struggling with the Dark Side.
Now I don't think there's a hard and fast rule that says 'black/dark clothes = bad or evil'.(Augustinian monks wear black habits, they're not evil, and we know that Jedi garb was partially inspired by monks habits) We see plenty of Jedi wearing dark shades of brown and gray. And Barris Offee wears black (though she might be a bad example considering she bombed the Jedi temple and framed Ahsoka).
But with that said, symbolism is a big thing in Star Wars. So when we see Luke's clothing go from light colors, to mid tones, to black. And those colors follow his arc through the story. I'd be inclined to think that there's something else going on. Plus we see similar things with Anakin and Rey.