My doctor told me its ok if your in a well venilated room. It doesn't get into you blood or even reach ur baby unless it gets into a cut. I know a lot of people say its not safe, but read up on it, I read a couple different articles that told me its fine.
They say that using hair color at all during pregnancy is unsafe. I colored my hair anyway, and my grandma told me that usually they say not to because the color won't take. But if you're really worried about it, ammonia free solutions probably are your best choice.
Im a licensed cosmetllogist...It is OK...but make sure you do it in a well ventilated. Also try not to rub it into your scalp. I also recommend that if you comb or brush your hair before coloring not to do it harsh. Any abrasions or scratches to the scalp will become irritated and may let the chemicals enter the blood stream and pass it to the baby!
As long as its ammonia free is not bleach and is not black then its safe to color :)