Unusual horse colors are a popular topic among visitors to this blog. Here is a short video of a dun Morgan horse that shows the characteristic markings and describes the bloodlines that carry this color, which is quite rare in Morgan horses.
The mare, Amberfields Lonesome Dove, is a shade of dun also known as grulla. She is from Amberfields Morgans; their website has more colorful Morgans and useful information. Thanks, Judy, for showing off your mare for the video!
Edited to add: Reader Nancy Castle posted a comment reminding me of a great resource for dun Morgan information: Dun Central Station It's a site I've visited in the past, but it had slipped my mind. Thanks for the tip, Nancy!