What Could A Painless Purple Line Between My Butt Cheeks Mean If It S Only Visible When They Are Separated?

Hi, Dear doctor i am a boy and i love looking at my body on the mirror and recently i noticed that i have a purple line from the top of my butt until the butt crack but its not visible unless the two butt cheeks is seperetad , as well I had no pain , no feeling about it , nothing it’s just bothering to see and i hope to get an answer for that as soon as possible