The tinting dyes are vegetable based so there isn't anything toxic to affect the baby.
However you are still putting yourself and your pregnancy at risk because
1 The changes in hormone levels affect your skin and entire system. A Mum to be may find herself nauseous, dizzy or feeling very unwell just doing normal things like drinking tea or eating something healthy. Mums to be can also have an adverse reaction to products that they never normally have a problem with. Lots of therapists for example find that they react badly to skin care products. So you could have a reaction to a tint even if you have never had a problem in the past.
2 if you were unlucky enough to have a reaction, the reaction could badly affect the pregnancy and even if it doesn't, an adverse reaction around the brow or eye area will be horrid
3 any treatment which might help tackle any adverse reaction will be potentially harmful to the pregnancy so you can't have it.
It is absolutely not worth chancing it once you understand the risks.