There are many opinions about whether you can color your hair while you are pregnant. Unfortunately, there are very few scientific studies on the effects of hair dye used during pregnancy. In some animal studies doses 100 times the amount of hair dye used in normal application showed no significant change in fetal development.
There are high levels of various chemicals in hair color. Low levels of these can sometimes be absorbed through the skin after being applied, and the dye is known to be secreted in urine. The larger danger in hair coloring lay in the fumes, which can be inhaled in greater amounts than will absorb into the skin. Perhaps the greatest risk of the fumes is that they make you nauseous rather than be dangerous for the baby.
There are certain precautions you should take when coloring your hair while pregnant. As always, you should first consult your physician for any recommendations. Second, make sure that you have your hair colored in a well-ventilated area. This will prevent the fumes from making you nauseous. Always wear protective gloves if you are coloring your own hair, as this will prevent the dye from being absorbed into your body through your hands. Rinsing your scalp with cold water can also slow or reduce absorbtion.
There are many "off-scalp" coloring methods, such as foiling and tipping that can be used. These methods, of course, do not reduce the amount of fumes that you will breathe in. If you are still concerned, you should ask your physician about these methods.