keeping specific dreads separated?

so here's the deal:

i currently have a section of my hair that's purple.
i just decided today to dread my whole head, as opposed to the half-head i was originally planning.
i want to dye the purple section blonde, but i want the dreads in that section to stay on their own; i don't want blonde hair swirling into my brown dreads.

any tips for keeping them separated?

updated by @niya-amity-haven: 01/13/15 09:27:23PM

just seperate them? u wont be able to control every hair or u will go crazy

--
My new book Ban The Taboo Vol 1

You won't be able to control every hair, but if you just tnr that section and through a bead on it, it'll help keep most of the hairs away from other locks