Purple Line Trick

This may seem odd, but I was researching ways to tell if your dilating/seeing if labor was near. I'm 35 weeks and getting so impatient. I found that there's a trick to tell if you're dilating. You look at your butt crack and it will be purple! Mine is not a dark purple but faintly. Has anyone heard of this? 
(Also I've been having contractions and not knowing it. Went to L&D the other day for pain and they had to slow them down.)