I wash in the machine at 40 degrees as that is the temperature I would wash a finiahed quilt at so it MUST stand up to that. Soap powder but no softener. I put a small piece of white cotton in with it, if that stays white then the job is done, if it's tinted, then I wash a second time with a fresh piece of white. I've only had to do this twice in my life - both times red batik. One piece I soaked overnight, washed again and it was fine, the other piece, I threw away as it wouldn't stop bleeding. Then I dry draped over an airer until just damp then press. I do not use starch at this stage as a) I might want to use a fusible product on it at one point and starch could stop it adhering and b) I've heard that starch can attract creepy crawlies into your stash. :-D
PS re the vinegar - my understanding is that this USED to work to set colours as dyes were natural-based. Now they are chemical-based, you need to use a chemical product like Synthrapol. The soaking mentioned above would have the same effect if plain water water were used - it is residual dye coming out of the fabric, NOT the colour bleeding.