Is it yellow or possibly tannish all over with just some darkness around the eyes? Does it have Brown anywhere else in the body? Does it have color in it's bill? Click on the different breeds here and see if a duckling is similar (a couple of them though don't have duckling pictures) http://www.metzerfarms.com/DuckBreedComparison.cfm
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Kind of looks like a mallard only more tannish than yellow. brown runs on a line from beak thru eye and into the back and dark streak one top of it's head.