Check out group costuming group called The Dark Empire. Uhm... URL is
http://www.thedarkempire.org/You'll need to register an account on their forums, but you can visit the WIP Costuming Gallery where members post their costumes as a work in progress. Lots of Sith and Grey Jedi costumes in there.
For colors, you will want to stay away from natural earth colors, like browns, tans, and greens. The base colors will most likely be black and grey, with some other darker colors for emphasis, like purple or blue.
Karate gi uniforms are excellent! As a matter of fact, the entire lower half of my costume is based off of martial arts. I have plain black karate pants and my shoes are tabi boots. If you can manage to shell out some cash, Mystik Merchants has excellent robes and cloaks for sale, some on the more expensive side though. Twin Roses Designs has tunics, tabards, and obi for sale and they can do things custom for you. I got my base outfit from them, and my cloak from Mystik and I could not be happier.
Good luck in your costuming endeavors! Please keep us updated on your progress. I personally love seeing the creativity of our members.
