A dun isn't really a color, but more of amplifier (?). The horse will have a base color, bay (bay dun; this one looks like a buckskin), chestnut (red dun), black (grullo) even buckskin (dunskin) and palomino (dunalino), but will also be affected by the dun gene, so it will show certain characteristics (dorsal stripe, primitive markings)
A buckskin is simply a single dilute bay (carried one creme gene). Some will have "frosting" as well. Genetically they are EEAACrcr, EeAACrcr, EEAaCrcr.
Yes she definitely has dark legs...it's strange, she posesses some traits from BOTH dun and buckskin it seems (just read about them both on another website), so she may be "dunskin"! She has the dark legs, the frosting in her tail (looks like highlights, it's cute!), dark tipped ears, and a faded (but there) dorsal stripe -- all of which are "primitive markings" that would point to Dun. But then she dapples out in the summer I'm told (and I can see dappling in certain light now that she's shedding her winter coat) and that's not characteristic of duns, it's more buckskin...and she's lighter than most duns I've seen, looks more like a buckskin. Hmmmm...I may never know...either way, she's adorable!
A clarification: dun or buckskin? Buckskin is not just another name for dun, although the term 'dun' was used for buckskins for many years (and still is, in some breeds). To see what a buckskin is, see the pages about the cream modifier, because cream acting on a bay base makes a buckskin.
A buckskin horse will have the same black points as a bay, but the body color will be diluted by the cream gene to a yellowish color of varying intensities. Most common is a clear gold, but the addition of the 'sooty' pattern may cause dorsal shading, strong dappling, blotchiness at the top of the legs, and an upper face mask. Sometimes these sooty characteristics are mistaken for dun, but if you are attentive, you can discern the difference.