I am bumping this question up, as I am also interested in protecting my gray/silvers from being discolored.
When doing a vinegar rinse, I only use WHITE. Have read and been told on another site apple cider vinegar has been known to stain the hair. Am not using products with colors added to the ingredients, maybe I am over-cautions but if it colors the product why wouldn't it color your hair. Violet, purple, and blue shampoos have the same effect I believe. Please correct me if I am wrong.