just read somewhere one should use an acidic shampoo after any hair treatment (alkaline) to restore the pH and thus closing the scales. since i have no idea if the shampoos i use are really acid enough (i don't happen to have pH paper at home) i thought doing a final vinegar rinse could be great for those mistreated hairs 

just thinking out loud since i will dye in a couple of weeks.

argh ... wish i could find that organic color systems dye by a miracle somewhere 

I've also heard that a vinegar rinse after a chemical process helps to "seal in" the process.  I have no personal experience with this, however.

Try using Lime Juice diluted in water... its doesn't have the odor and it is just as easy.

Products are made now to close the cuticle.  Schwartzkopf's Herbal Sealer and Aveda's Color Conserve and best of all is a Product called Fire Out from Stevens Research.  Do a search on Stevens Research.  Best of luck.  www.stevensresearch.com

Color companies have figured this problem out.

Vinegar will only remove a nominal amount of color.  I accidently dyed my hair a very vibrant red once and tried a vinegar rinse (full strength) to see if would help get some of the color out.  I did see some color go down the drain but when I dried my hair it did seem to have changed the color at all.