It seems like, before someone went over it in a darker ink, this nymph's nipple (viewer's right) was red. Or a red dot was added on top of the dark ink. I'd find it interesting if it were red, but since the ink has faded it's hard to see. What do you think? Also, if it is red, would this be the only nymph with such a feature?
I shifted some values in photoshop that seemed to bring out the color more, and noticed that it does appear to be the same pigment as the blush on the cheeks. Maybe someone with more image editing skills knows of a better way to test this.
PS: this is important but I'd like to know your opinion before explaining why.