I've been reading up on this subject of late as I'm needing a dye job right now to cover some greys but most books recommend not doing it in the first trimester. Basically the books say no studies have really been done on the effects of the chemicals contained in the hair dye so best to avoid it. If you really feel you must they suggested to get foils as the chemicals will not hit your scalp, therefore cannot be absorbed into the rest of your body.

Due to my history I'm not taking any risks so will wait until another 4 weeks at least before I color my hair.