I see that someone else has pointed you in the direction of Shout's Color Catcher (Laundry Aisle)
That really is your best option. White Vinegar may not really be a solution for a commercially dyed yarn. "Back in the day" and even today it is used to "set" dyes on animal/protein fibers (wool, mohari, silk, etc) it was not used for Vegetal fibers (cotton, rayon, etc)
Today's chemical dyes are formulated differently and all the Vinegar does is act as a rinse aid, but not a setting solution.
If you keep separate pots for dye work, you might also find that simmering with a dye catcher is less wearing on the newly completed product and has the advance of risking loose dye from other items in the wash load.
Here is a link to a blog post about making your own - you can sometimes find soda ash in craft stores - ev en the left overs from one of those tye dye kits can make quite a few.
Enjoy The Making