When you say safe what exactly do you mean. I've got dark hair, and I've dyed it several times (mostly red) to no ill effects. You want to be careful and keep it healthy. Dont over dye it. But really as long as the professional knows what they are doing and is careful (and you dont have any unusual reactions), you should be fine.
well my hair is dyed black and if i get it stripped i understand that i would have to keep dying over because my roots would come in white/blonde so i wanted to know how high the risks of it going patchy are?
If you get it done professionally, yes. Hairdressers tend to know what they are doing and use a lot of treatments in between the bleaching to keep your hair in a good condition.
oh, i didnt know it was already dyed black. Honestly a good hairdresser should be able to prevent that.