Smoky brown, technically, but the majority of people would call him buckskin. The difference is that buckskin is bay + cream, where as smoky brown/brownskin is brown + cream. Brown rather than bay is what is causing him to be so dark and change so much over the year.
A sooty buckskin is actually different than a brown based buckskin as they're too different genes. He looks like a brownskin though, and a drool worthy one at that! he is what Henny should aspire to look like LOL. Posted via Mobile Device
Among other genes, I do with there was a sooty test because I would test my mare for it. For whatever reason, when she sheds her winter coat, she gets little brown hairs all over, particularly over her hips, withers, and the underside of neck along with some on her cheeks. Now, which you'll see from the picture below, she doesn't look like your gelding as much as she just looks like she's in terrible need of a bath. But it shows the difference between what would technically be considered sooty buckskin versus smoky brown/brownskin.