dyeing dreads

My daughter dyed her tips blue a year ago and since then has dyed all of her dreads back black to have them one color. However the dye doesn't get all of the hair dyed. Does anyone have suggestions on how to get uniform color without damaging her dreads and without going to a salon?

updated by @lisa-wade: 01/13/15 10:04:57PM

Depends on what you're doing. I know with bleaching if you do little at a time, a few times over the course of a week or even up to a month you can get it all covered, but the damage it causes isn't really worth it and it's hard to wash it all out, seriously hard.