As long as I use the same colour and brand I never had a problem, when I tried to dye my hair brown it went black and faded to deep red go figure! I wasn't preggers at the time though. I dyed my hair at 3wks preg and was really worried my local dr at the time said it was perfectly fine to dye your hair. I moved suburbs and found a dr who knew what she was on about and asked her and gave her the packet I intended to use and she said it was perfectly safe as did the chemist. I found that article and thought it would be of interest as it seems to be a commonly asked question. My mum bleached, smoked, drank (a little) and is a caffiene addict the drs said I'd be a small baby but was nearly 9lbs and 24inches long she said if that was small she was happy she didn't quit lmao