Like someone already said avoid Rit dye. Also avoid
any dye you find in the grocery store (and maybe
Jo Ann fabrics as well depending on their selection).
You probably will have a hard time finding good
permanent dye locally unless you live in a textile
region. Look on the internet. Once you find it,
buy 2 or 3 times as much as you think you will
need. I can guarantee you will want to start dying
other things once you find how easy it is, and how
well it works.

Also the directions may say a "mordant" (to set the
dye) is optional. It isn't.