I have had mone done twice - dark all over dye. The hairdreser said to me that they can't guarantee that there's no risk - but then that is the same for absolutely everything.
Like everything else - how many women will be doing therse normal things up to 2 or 3 or more months pg becasue they haven't realised they are pregnant - and there's no harm done?
She said if people didnt dye their hair you wd see women walking around everywhere with 9 months regrowth.
Anyway I just went ahead didn't worry about it.