Yep, dun is never hidden but can be misidentified. I've seen duns that are so dark they are easily mistaken for bays.
and I don't care if 75% of the horses in a pedigree are dun, if the horse in question is not dun they won't pass it on. That's one of my biggest kolor breeder pet peeves. When they say a certain mare or stallion is a color producer or has "lots of color in their lines" and it's a plain old bay or sorrel. Or mention that their (bay or sorrel) stallion is a 67% color producer but when you look at their broodies you quickly realize all the color is coming from the mares.