Back to brown (sob sob boo hoo)

Don't worry, I'm not entirely giving up on fun hair  😛

I'm going to grow my hair out again (but keep the shaved sides) and to help me in this effort I'm going to make a new set of wool dreadlocks.  Dark brown transitioning to all the colours!
I installed my old blue ones but it looked too odd having dark brown roots and faded minty blue on sonic the hedgehog blue dreads!!
I could dye my hair blue but I don't want to bleach again just now so I'd still have the 2-inch dark brown root problem.

Get to the point wumman!

Does anyone have experience of Adore's Darkest Brown or Mocha dyes?  Do they transfer or run much?  I'm a little concerned in case the brown dye bleeds onto my (planned) rainbow ends.
What happens if brown dye is applied to blue hair?

Slight change of plan; I'm going to re-dye my hair blue, put the blue dreads back in and just live with the brown roots for a while!  I have another project to finish before I can start making new dreads.