Shink,
I forwarded your question to Richard Schultheis, KDWPT Migratory Game Bird Specialist, at the Emporia Research & Survey Office.
His reply is below.
Craig
It looks to me like that is likely a leucistic hen mallard as the hunter suggested. Leucism is a term that is generally used for birds that have some component of diluted or reduced pigments in their feathers. It is a bit different from albinism, which is lack of pigment in the bird entirely, but you might think of it as along that gradient. Leucistic birds will generally show some color, but it will be pale or washed out in appearance. It is a rare condition, but we do see them occasionally during surveys, as they are pretty easy to spot. A google search will likely provide a number of images of leucistic ducks and other birds for comparison.