Yes, Luke is dressed in black in Jedi to deliberately show how close he is to letting his fear and hate overwhelm him and that he is basically on a razor's edge and could turn to the Dark Side within a moment's notice.
Luke suffers. He suffers hate, for his father who cut his arm off, angst for Obi Wan who lied to him about his true heritage, fear that his sister Leia will be Palpatine's next target, and fearful that all will be lost.
But all turns out well after Vader throws the Emperor down the shaft that's an inexplicable safety hazard in his throne room. So if Luke wins his fight against Vader and then turns his back on the Emperor's offer to join him, how do we really know that Luke is not joining the dark side?
Take a look at his costume. Look at the fold that is now unbuttoned, what is that colour? It's white. It's the yang to black's yin. Underneath all Luke's stresses, he was always the good guy. Always the Knight in White Satin. Always the boy who never got to Tosche Station to get his power converters. He was a Jedi, like his Father was before him. Nice symbolism Lucas.
This flap of white was a very subtle point and perhaps lost on many a viewer on first watching of the film. This was indeed a subtle moment and in the long run it was not lost on many Star Wars fans, so when George Lucas got around to writing Revenge of the Sith with Johnathan Hales, he made an even better reference to light and dark.
|Literal foreshadowing in Sith|
It's the last time the two Jedi will indeed talk to each other as friends. Look carefully at the lighting, Obi Wan is in the light and Anakin in the dark. Yin and Yang. Good guys and Bad Guys. Jedi and Sith. While everyone piles on the hate, Star Wars purists should remember how good Lucas really is. Sometimes it's not just about story, it's about great film making.