P.S. The one major visible (there are others but they are not always present) difference between dun and buckskin horses is the presence of an "eel" or "dorsal" stripe. If the horse you saw had an eel stripe than she was definitally dun. If she didn't then she was buckskin.
Actually, this is not completely true. The smutty/sooty gene can create "countershading" that can mimic the dorsal stripe. Its not as clear as the dun gene, but it can still create confusion on telling a dun vs buckskin apart.
Its also possible to have a buckskin dun, so dorsal stripe can actually be evident.
Could it have been a Chocolate Palomino or some call them smokey palomino ? Its hard to say without seeing it or a picture. Here is an interesting link http://ultimatehorsesite.com/colors/palomino.html
The mane and tail are usually off-white (flaxen) but can have golden hairs or black hairs. Sometimes the sooty gene will create a 'gray' mane on a palomino.
This AQHA Mare (Northwind Gold, owned by Mikie Peebles) shows an unusual distribution of sootiness on a palomino. The mare's rear end has been darkened, and the barrel area dappled, but the neck shows her base color.
Ramblin' Lemon Twist -Missouri Fox Trotter stallion owned by Lee Yates. This photo shows the deep dappling that can occur on palominos.
The most beautiful horse I ever saw (color wise) was an appy. It had a dun colouring that bordered on palomino as the coat had this golden sheen. It was a blanket appy with a very straight blaze and black points on the ears and muzzle. The mane was black and the tail was black also and the haunch had these lovely golden/dun spots set on a white background.
All four legs had stockings then black at the knee/hock area then merged into the basic gold/dun body color. Could jump the moon and he was about 16:1 or 2 hh.
I have never seen anoth horse that had these markings after him.
As a stallion he never reproduced all of his stunning color points but many offspring had parts of him
Could she have had something like this? I just found this yesterday while I was looking around......................Well, I just read the op and you said her mane was that color too. IDK then.
Take the coloring of the first horse and the pattern of the last 2 horses, and that was it.
Sounds like you are for sure asking about a Dun. As for the breed none of us can actually say for sure, as some breeds are prone to odd colorations as was pointed out in the arab. Also, Dun is a color and registration, so as for the color, it can happen in MOST breeds, with a few exceptions. The tail and mane color can happen, its all genetics...but the dark, prominate dorsal stripe is a tale-tale sign with little exception.
The silver gene on a black based horse causes a light mane and tail and chocolate body:
If it also had a dun gene it would have a dorsal stripe. But I can't find a picture on the internet of a Silver Black Dun as it would be called...
OR...
Another silver gene at work, Silver Bay:
Add that with a dun gene and it also sounds like what your talking about.
As I'm pretty sure this is more common than a mutation of arabian, I think this is more likely. Also although these pictures are all of miniatures this gene is present in other breeds.
That gene is relatively common in Icelandic horses as well (especially in them outside Iceland since it's a pretty colour and horses like that are often exported, heh..)
Here's a really pretty silver on a black base Icelandic stallion, you can get blue dun (grullo) with silver dapple as well, altough I couldn't find any photos of that.
Sounds to me like a tri colored buckskin paint mix with different kind of breeds and what not so that means depending on the breed, it depends on the color!
