Parsing through what I've been able to of the after-the-fact interviews and recollections -- from when the movie came out to today -- Mark's concerns were when he read the script and saw his own costume concept art. Stuff like this:
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Enh. Retcon. She wasn't intended to "go bad" when she was added as a background character in AOTC. And I'm not particularly thrilled with
that take on why the character wasn't back in ROTS (even Luminara's screen time was all but eradicated for the latter). So the black there is, again, not deliberate foreshadowing.
Yes, and. He wanted to present himself to Jabba as a Jedi Knight. He scavenged stuff from Obi-Wan's home to make his lightsaber. And it's Tatooine. Since they all dress like that there, he could easily have found something approximating Old Ben's robes if that's what Jedi look like. Anakin's a whole kettle of fish I won't get into again. But in general I have seen a lot of ball-dropping from the mid-'90s on. Much on George's hands.
Except, when you can watch it on a bigger screen, that's the post-Vader-capture version of the costume. No tabard or sash, placket hanging open showing the light facing. George is addressing what Mark is wearing
there -- black tunic, fitted pants, and knee boots.