I ended up buying 6 yards of trim on ebay, after the very convincing argument of $0.97/yard.
Here’s what it looked like:
So I pulled on some rubber gloves and my best mad scientist expression:
I used about 2/3 a packet of purple RIT. I also bought some fuschia RIT, since all my fabrics are on the redder end of purple (rather than blue), but turns out that the pure purple RIT was the exact color I wanted and didn’t need extra pink.
I also balled up some white tights and tossed them in the pot:
SCIENCE! Good for historical costuming and badass tights!