As I was growing up my mother always added salt to the water when hand washing clothes that bled dye to "set the color". I've also heard about adding vinegar. Unfortunately, neither will work on clothes that have already been dyed. Don't waste your time or resources.
There is some history to the salt and vinegar stories. When you dye cotton yarn or fabrics, salt in the dye bath does help the dye absorb into the fabric instead of staying suspended in the water. For wool or nylon, vinegar does help the dye absorb. But neither is a dye fixative for already dyed fabric or fibers.
So, what can be done? There are commercial dye fixatives that can be purchased for home use. Brand names include Retayne and Rit Dye Fixative. However, these are intended for use by artists and companies that dye fabrics and understand the type of dye they are using. Dye fixatives are cationic, which means that they have a positive charge. The positive charge allows the fixative to cling to negatively charged dyes, such as the direct dyes and acid dyes. They cannot stick to basic dyes, which have a positive charge, and have no benefit for colorfastness for that type of dye.
Best advice for that blouse or jeans or socks that fade?
Will the clothes ever stop fading?
Maybe. Some do stop releasing dye after several washes. But be careful, don't trust them completely. Higher water temperatures may cause the release of dye even after a few years. Never wash an unstable dyed garment with any clothes you care about.
Specific questions? Just ask here.