One thing everyone agrees on is that you shouldn’t color your hair during the first three months of pregnancy. While there is no real data showing harm, this is a sensitive period during which the baby’s organs are being formed, and toxic substances could pass through the mother’s blood into the placenta and into the baby. (In animal studies, at doses 100 times higher than people generally use, no significant changes were seen in the fetus.)
Even after that, it’s recommended that you use gentler semipermanent tints rather than harsh permanent chemical dyes. Maybe it won’t be as hard for you to revert to your natural color when you realize that a pregnant woman’s hair generally becomes stronger and shinier.
A good alternative to hair dye is henna, which come in different shades: the familiar red, and also for dark blond, brown and black hair (although special precautions are called for with black henna). Henna can give your hair a beautiful, warm shine that washes out after a few shampoos like a tint.
But make sure you read the fine print on the label when you’re shopping: You’re looking for products that do not contain synthetic dyes or color enhancers such as sodium picramate. You should be able to find pure henna in certain health-food stores.