just guessing from the pix but looks like lacing starting, i see a darker pattern and then white too. I have lacing on appys, solids and pintos at my house,LOL.
It's the start of lacing, which is considered by some to be linked to Sabino, and others to Appy- since she has an Appy background- well, to be honest the only other time I've actually seen this, as opposed to pictures, the filly has a Leopard/Blanket dam!!
So...on this question..my silver dapple/pinto filly has white coming in on her back right behind her mane, looks like frosting or something...what would you call that?? is that lacing?