Danl,
The purpose of the vinegar is to "set" the dye, so that it doesn't wash out.
Maybe "a little vinegar" is not quite enough. I would use at least 1/4 cup
of white vinegar to 1 qt. of dye bath. I have never added salt to any of my
dye baths, except that in the dye powder.
Best-


"If I have been able to see over the horizon,
it is because I have stood on the shoulders of giants,"
Sir Isaac Newton

snip
some salt and a
little vinegar. I don't know why, just read it somewhere.