Under usual circumstances, the cervix is pink (cervical pink, now there's a new crayon color just waiting to be invented). With pregnancy, blood flow to the uterus dramatically increases, resulting in the cervix developing a bluish tint. This color change is referred to as Chadwick's sign, which can appear as soon as 6 weeks after conception . Ok, ok, so maybe this is not the most convenient way to gauge whether you might be pregnant, unless you are hypermobile, or have an exceptionally curious partner, but still, it's quite fascinating. Plus, cervical self-exams are completely possible (more info available at: http://www.beautifulcervix.com/participate/).
A woman's total blood volume actually increases 30-50% during pregnancy, so it's no wonder that this can make your cervix a little blue.