Do you know if she's had a foal before? Can you take a photo of her bag?
At this point, it's just a guess that - yes, she is. But you need to keep checking her bag and see if you can get liquid from her teats.
Feel her butt muscles. They will soften up like jello when she's close. And the liquid will start feeling sticky as she gets close.
When she's eating, place you hands around her middle for foal movement. If she is indeed pregnant, her side to side "watermelon" look will drop down under her belly at the very end of her pregnancy...as the foal begins to prepare itself for birth.
I don't know about your Appy color questions except to acknowledge that your girl is obviously an Appy! LOL. There are many appy breeders on here that can respond to that.
Kuddos to you for adopting this lovely girl!
PS: In doing your homework about pregnancy, etc.....don't hesitate to peek at our "Health Pages" on the subject at
http:www.miniature ventures.com