In the meantime bear in mind that the difference is usually only noticeable to you. If you feel really self-conscious you can pad one side of your bra. Even after puberty's over, most women's breasts, like the two sides of our faces, differ somewhat from each other. I have a friend whose nipples point in different directions. And kind of cute, too.
Nipples come in a whole range of colors, from light pink to brownish black.
The color of your nipples usually corresponds to your skin color. You've probably got darker nipples. This, too, is normal. Sometimes only one nipple is inverted. Sometimes they invert or correct themselves during development.