The difference is that the horse you have posted, verona, has white markings over two of the places dun factor can be seen (shoulder barring and face cobwebbing) and you can't see the legs to see barring there, nor the back of the ears to see tipping. You can, however, see a distinct dorsal. Poseidon was referring to the OP's horse when she said there was no dun factor.
I was not being sarcastic. Dun markings do not just come and go at random or pick and choose. Either they have them or they don't. And that dunalino overo has a pretty obvious dorsal stripe and the OP's horse does not have one at all.
The OP's horse is definitely a sooty palomino, the less distinct, smudgy dorsal stripe, seasonal color change, and the typical countershading all point away from dun. IMO, the OP's horse does not have the dun gene.
A palomino dun horse will look just like a pally, but with dun factors. There isn't major color change to the palomino coat. Yes, the dun factors may look less obvious due to the horse having two dilute genes, but there won't be such a dramatic color change as the OP's horse.
I'm loving this input! He is of gaited breeding, and I have no idea what his parentage is except for a photo they gave me of his granddad who is the spitting image of him.
I would love to know more about where the mottled skin comes from. I've had folks with rocky mountain horses ask if that is what he is (in the spring time).
As for more wether or not the dorsal stripe stays there year round, it does but he fades out pretty bad by August just like any other horse would. He doesn't have zebra markings, but he does have black points on his legs. He also has black hairs in his mane and tail.
I will conjure up some pics of this (eek - back to the pile of cd''s!)
The pics of the halter horse - has he been body clipped maybe?
Here's pics of the inside front leg and his back - and this is from just 10 minutes ago from where he stands in my back yard, and this is how he'll look thru the rest of the year - I appreciate everyone's input! And he does have some faint stripes on the insides of his knees - probably easier to see just after a spring shed out, but they aren't radical markings by any means. I will mention that his dorsal stripe is a little more obvious after a body clip, too. It is never completely gone.