Yay, congrats on your pregnancy! Yun ang linea nigra talaga, nakita ko rin yan sa sarili ko, parang dark line lang from belly button going down, kaya don't worry, super normal lang yan! Ang purple line or linea nigra ay sign ng dilation pero hindi siya reliable 100% kaya best talaga na i-check mo with your OB during your regular checkups para sure na alam nila kung gaano ka na dilated, lalo na if you're getting close to your due date.