Molly is a mix, right? So you aren't going to know for sure what she should end up like. But my pure bred black girl did develop a noticeable brown mane down her back from her neck to her tail at around 8 months or so. It all fell out when she shed the next spring but it was definitely brown. Our breeder said it happens sometimes and equated it to cradle cap in babies, human babies. Not the same timing but the same effect. Plus the black ones will often look rather brown when they are about to shed.
Bites, dunno. How do you know for sure they aren't flea bites? What about ant bites?