Purple line & dilation

Anyone know anything about the purple line that shows up in your butt crack when you're dilating? (Sorry there's really no other way to say it lol) I was just googling it and was wondering if any ladies found it to be true. If you don't know what I'm talking about here's a couple of websites.
http://birthwithoutfearblog.com/2013/06/06/alternative-methods-of-checking-dilation-the-purple-line-and-more/
^this shows some pictures.
http://www.scienceandsensibility.org/the-redpurple-line-an-alternate-method-for-assessing-cervical-dilation-using-visual-cues/
^this article shows how to measure the line.