Definately safe, as long as you are in a salon as there products are alot safer and they will have good ventilation. Im a hairdresser and if it wasnt safe to be around hair dyes etc i would be worried. Congrats btw :)
I waited until I was 14weeks with my first and now 2nd I keep the doors open and bathroom fan on I wouldnt do it to often but thats just me:)
I have and had dyed my hair while pregnant. With my first second and also with my third lol nothing happen to me or the baby. Just try not to smell it too much. :)