Of course they're real; you've just posted a picture of one! Also known as red dun. There are various iterations of dun/buckskin, it is one of the "primitive" original colours of wild horses.
Difficult to tell if the top one is a true dun or rather a bay with a prominent dorsal. There isn't much dilution in the coat but you'd need a good shot of the eye tips and tail head. Photo editing and filters can really change how coats appear.
Easiest to think of ‘dun’ as a pattern laying over the base colour, causing dilution and dark points. Any base colour can coexist with dun; you can get grey, chestnut, palomino, various roans, various white patterns and the rest all with the dun on top.
What we were mostly taught as dun, yellow with black mane and tail, is normally a buckskin ie a bay with one dilute gene. Common in welsh and sadly declining in Connie’s.
Can’t tell on the horse in the top pic, need some close ups of ear tips and dock to be sure. May just be a bay with a stripe!
Hermosa looks bay, but apparently, she doesn't have the bay gene. She has a dorsal stripe and looks very light in summer, but much darker now. She has a gene called nd1, which means 'not dun 1.' So I don't even know. I think she's 'bay' or 'dun' on various bits of paperwork.
Ah, I was going to say your mare looks brown to me, not bay, Caol Ila.
But then I saw the second pic.
[scratches head]
Regarding the first photo of the QH, I don't know what he is. Dare I say I'd want to see him in the flesh, see his parents, his great gandparents, his great, great grandparents, and have a horse colour guru with me.
Here’s hermosa’s big sister. She does have a prominent dorsal stripe, but I don’t have a picture showing it.
the sorry state pre-clip photos are from her stay in the hospital, it shows her darker legs. She had primitive stripes on her legs when she was younger.