Hey! I saw your ask to bunjy and I tried to tag you in a reblog, but it didn't seem to work. Your mom's horse sounds an awful lot like a bay or "classic" dun.
My knowledge on horse genes only extends to HARPGs in DeviantArt, but Dun has always been a gene I love to play with because of how it dilutes the coat without whiting it out.
She’s definitely not bay - I’ve ridden a WIDE range of hues for bays and she falls way outside that range. Looking at the Wikipedia article for Duns, she’s definitely that - most likely a bay dun, though maybe with another lightening gene in there bc she still looks a decent bit lighter to me than the bay dun examples I found. She has some transversal stuff and zero face darkening though, which is cool to know about now that I’ve read about duns!
Thanks for the tip - now I’m wondering if her bay filly will do the Lipizzaner thing of lightening as she ages and turn into a dun like her mother.
Edit: just realized you weren’t saying she might be bay but rather a bay dun aka a classic dun XD