Two of our yudansha use the Japanese cotton indigo hakama, which stains other people's gis a lot. We complain, but there really seems to be nothing to do; indigo is like that, even if they try to fix it with vinegar and whatnot. We just wait out the month or so it takes for the staining to stop.
Vinegar doesn't "fix" indigo. It might conceivably help the fabric shed the massively excess amount of dye applied to it, but probably no more than simple wash/rinse/repeat will.