I'm pretty sure she's just a flaxen sorrel with counter shading. Reasons? In the pics form the first post - her legs are more golden - something commonly found in mealy/flaxen chestnuts. I do not think she is a dun, or a palomino.
I believe she's just a light sorrel with a flaxen mane and tail. I have one in the pasture that looks just like her.
Hmm I think I'll skip the tests. It's not that important to me what color she is (I just find it interesting), but thanks for the input! What's counter-shading, by the way? Does it just occur as a stripe along the topline, or does it have other forms?
Counter shading is actually just another form of sooty or smutty. It can appear in many forms, sometimes altering the entire color of the horse, and can often present false dun markings such as dorsal stripes and zebra barring.
Example of a bay Arabian with countershading making him look dun:
It's typically the only cause of these markings in non-dun horses. However, it can take extreme forms such as this one, referred to as sooty: