My sister is a hair dresser, and I am ttc, so I have asked her this one already.
Basically, as long as you have your hair foiled, as opposed to doing a full color, you should be just fine. Even bleaching your hair is ok, because the stylist can just use an off-scalp bleach, which means that the color and/or bleach will neve touch your scalp, and, therefore, not be absorbed into your skin.
My friend is a nurse, and she told me that the reason you are advised not to get your hair done during pregnancy is because your sense of smell is so heightened, that you will probably throw up due to the smell. There really isn't any risk to you or the baby from the color.
So, if you don't mind feeling a little woozy, you should go for it! Good luck!