I'll confess I haven't done this yet, though I do have several never-used ties that obviously do not need to be washed, so won't be exposed to a color fixer such as Retayne.  Some thoughts:  The polyester ties do not need to be prewashed, as the ties will not bleed color is the finished project is washed.  Silk ties are another story, as dyes in silk ties can bleed.  You can test small pieces of the ties by soaking in water to see if the dye bleeds.  If not, you can use them safely.  If they bleed, you can soak with a small amount of dye fixer in water, then dry before use.  Or you can dry-clean the finished project.