What Causes Discoloured Circular Area On The Top Of Vagina?

Hello- I'm a 25 year old female with no history of any STD's and never been hospitalized for anything other than giving birth, twice. I have a small discolored circular area on the top of my vagina where pubic hair grows. It almost looks like a ringworm, but I know it's not one. It doesn't cause me any discomfort or anything.. what could this be from?