The sire is a resistered brown. He does have one of those weird white markings though...let me see if I can get some pictures up of him.
Here we go. Right over his eyebrow xD
Heres a full body shot of him...sorta xD pardon how wet he is, he'd just had a bath/leg treatment (he pulled a tendon last month). He's old, fat, and still has winter fluff- but under all of that is a gorgeous stallion. He competed actively in Halter and Driving before retiring ^^
I think it might just be a crap shoot on whether the foal will be colored or not. Part of it depends on the parent's zygosity for color but the other part is just luck.
As for the white on her spine, my first thought was scars from an old injury as well but since you said they were present at birth, I bet they are just how she is exhibiting her pinto pattern. Their placement and uniformity does strike me as very odd, but some pintos do have very strange coloring .
They are big enough for her to be considered coloured. However, being along her spine like that, with no other while present, I would wonder if they weren't from old injuries to be honest. How long have you had her?
Well it took a bit of work but I got to the skin on three out of the four (or five if you count the leg) spots xD the skin was pinkish. That generally means that the hair is white because of pigment, and not injury- right? The leg spot has skin that's more of a greyish shade though.
I'm not going to lie. I would LOVE a chestnut paint, although the chances of that are slim xD any color will be great though. I'm sure that either way, the foal will be lovely.