I always thought my Mustang was black that faded to a seal brown. But he's never faded quite like most other blacks or browns. Blacks only fade in the summer, and very minimally. Browns can be almost solid black when their new coats grow in but they still always have that telltale brown area around their muzzles. Brego gets a little gold around his face and then it goes away. And he's always shown odd patterns and colors in odd places and tends to fade more gold than red.
Someone once suggested that he might be a very sooty dun or possibly even buckskin which I thought was ridiculous considering when he grows in a fresh coat he looks like a true black.
He's so dark that it's hard to really look for any of the telltale signs of the dun gene, but he does have some of the more classic markings like the wide dorsal stripe (which I regrettably don't have any photos of) and face mask.
I still have no idea. I think the only way to know for sure is with a blood test.
HOWEVER, I remembered a photo I'd taken a long time ago to document his freeze brand. It was winter and his coat super thick making it near impossible to read the brand, so I clipped just the small area. I hadn't thought anything of it at the time but now that I look back at this photo...
Do blacks and browns normally clip to that color?? I'm really curious to see what he'd look like if I did a full body clip on him next winter.