they'd obviously drop feathers and maybe also duck breast/meat. oh and maybe rhunic ppl can make it into beijing duck. colors would be black/grey/blueish with white or white or black or maybe yellow also or any combination of these colors rlly. i think it'd be cool if they look as derpy as possible lol, or atleast a yellow derpy version as one of the possible skins
If ducks do get added, I think they'd either be white domesticated ducks (in regions where farm animals spawn) or wild ducks with mallard-like textures -- maybe black ducks, eider and other textures could be added too.
I'm sure Ithilion can name far more ducks than I can and texture them.