Same issue here.
I've been through the desert with a horse with no mane.
I am sorry, but I simply cannot comprehend bugs like these.
I have been playing 1.10 with Hearts of Stone for hours and Roach was fine. I called her after the wedding and she was black and without a mane.
Now, if I travel to White Orchard, Roach looks fine, textures and mane are there. But if I go back to any other region, she is bugged again.
Mods that replace Roach do not work.
WHY?
How on Earth does the region affect the look of Roach? Why are the game assets so intertwined? Why do we have to deal with annoying little bugs like these?
I really like Eastern European developers like CDPR and Bohemia Interactive, as another example. They truly make great and ambitious games. I just love the fact that in Witcher 2 and 3 farm animals behave like they do in real life, because the devs are not metropolitan shut-ins, who only had the chance to see a chicken in KFC, BUT my God, Eastern European devs have problems with coding game engines and ironing out bugs. Not that Bethesda is any better, but still.
Don't take this the wrong way, I am from Eastern Europe myself, and I love this game and CDPR, but sometimes these little, puzzling and immersion breaking bugs can get really annoying.
I wouldn't mind it much, if there were frequent hotfixes, instead of gargantuan patches every few months, that may or may not fix specific bugs.