The color of this guy is like photos I have seen of mules, but I’m guessing he is a dark grulla?
I was looking up photos of dun horses the other day, and some are fairly dark even without being grullas. Given the warmth of that horse’s color, I wonder if it isn’t a different type of dun. All the ones I’ve seen called grulla were grayer. But I’m not an expert, that’s just the impression I got from a google image search and reading a couple associated pages.
My keyboard is broken. I keep pressing "Escape", but I'm still here.