Buckskin is commonly misclassified as 'dun'.
A buckskin horse is a golden colour, with black points (mane/tails/legs/nose). It does NOT have a dorsel stripe, leg barring or cobwebbing. Those are factors of the dun gene. So a buckskin with a dorsel stripe would be a dunskin, or a buckskin dun.
Buckskins are produced when a horse carrying the dominant cream gene (cremello, palomino, buckskin or smoky black) breeds with a horse that carries the bay gene.
for more info on horse genetics, look here:
http://www.animalgenetics.us/CCalculator1.asp
A buckskin horse is just another name for dun. A creamy/chestnuty colour with a black mane and tail, sometimes with black socks as well
Here is what the International Buckskin Horse Associationhas to say
A true colored buckskin should be the color of tanned deerhide with black points. Shades may vary from yellow to dark gold. Points (mane, tail, legs) can be dark brown or black. Buckskin is clean of any smuttiness. Guard hairs which are buckskin colored grow through the body coat up over the base of the mane and tail.
Dun is an intense color with a hide that has an abundance of pigment in the hairs. The dun color is a duller shade than buckskin and may have a smutty appearance. Most dun horses have dark points of brown or black. Dun horses sport the "dun factor" points which include dorsal and shoulder stripes, leg barring, etc.
and her is what the American Buckskin Registry says
BUCKSKIN: Body coat some shade of tan, from very light (creme) to very dark (bronze). Points (mane, tail, legs and ear frames) are black or dark brown. Dorsal not required.
DUN: Body coat some shade of tan, from very light (creme) to a dull or smutty brown (earth tone). Points, dorsal stripe and other dun factor markings are dirty black or smutty brown. There are many shades and variations in the dun color. Dorsal stripe required. Note: The buckskin colored horse with dun factor (dorsal stripe, leg barring, ear frames, shoulder stripes, face masking and cobwebbing) is the ideal color that ABRA was founded to preserve over thirty years ago.
Here is a list of the Dun Factors
Mottling - reverse dappling, sploches or dark smoke, can be found on the forearm, gaskins, shoulders and stifle
Dorsal Stripe - dark line down the back from withers to tail
Shoulder stripes and neck stripes - markings on the neck and shoulders may either be single or multiple lines often combined with dark patches, called shadows. These also are on the withers.
Leg barring is some times referred to as tiger stripes or zebra striping. They maybe found on both the front and back legs.
Frosting can be at the edge of the mane and base of the tail, and may also be intermixed. The base color of the mane must still be dark for the horse to be considered a true dun.
Masking is dark shading on the muzzle that extends up toward the eyes. Most horses have masking on the bridge of the nose, but it can extend around the horse head on to his jaws.
Cob webbing are lines of dark color that start on the forehead and may extend down over the eyes.
Ear tips are a darker outline of color around the outside edge of the ear. Some horses may have shadows of color on the back of their ears, or even pronounced horizontal stripes.
You can find the link where I got this information in the related links
