I bought their mohair girthbelt last year. I used brown Rit dye with hot water and salt added (as per the recommedation on the box). Then I stretched it out end to end on a wooden board using screws so it could dry for a day. Look a some other threads here to see how others belts were stretched out. This worked for me.
I'm doing an ESB Fett so brown was good for me. I'd wait for more responses on what color dye to use for ROTJ/ SE. Good Luck!