I think you need to describe your problem better. Is it just a darkened area that is there all the time or only some times? Does it hurt or itch? Any bumps? Exactly where is the area, above your vagina, below it, to one side?
Some people do get natural skin darkening in the genital region. Apparently genital-region skin just sometimes does this for men and for women. Sometimes the abrasion of wearing menstrual pads will darken the top inside of the legs. I don't think darkening alone is an issue. If you don't want to talk to your dad about these things, see if he will get you signed up for a woman ob-gyn, so you can have someone to talk to about questions like this. My first pelvic exam was done by a silver-haired lady doctor with a Southern accent who called me "Hun," and I was always so grateful.
I was just looking on the Betty Dodson site because we've had several vaginal-lips questions on the site this week, and right there on the intro page in her gallery was a photo of a vagina with, in essence, neat little brown edges. It reminded me of a Siamese cat. Every vagina on her gallery is a normal one. Here's the link (delete spaces):
dodsonandross . com / genital-art-gallery-artists-statement
I'm a white woman and my husband is white I noticed today that my vergina is turning a brown color we don't have sex that often and was wanting to know what is going on with me