Black area on inner pink vaginal lips?

Hi I'm 31 female. This is a bit embarrassing but since no one knows me here goes. This morning while showering and trimming my private area with a mirror o noticed that inside my vaginal lips on the pink part there is a black area. It's about the size of a pencil eraser but not symmetrical in shape. It's fat on the skin, it's not raised.... All the other area is pink so this is easily noticeable. I don't know if this is a new thing or not as I have never looked there with a mirror before I don't know why I happened to today, what could this be? Is this something to be worried about? It's nothing do do with shaving ect as as I said it's on the inner lip area. I would appreciate any advice info etc thanks