for the lighter feather edgings (to start): mix of raw sienna, with a touch of burnt umber, a touch of raw umber, and a touch (careful!) of orange. Add a touch of white as needed to get correct shade............
this was passed to me by another carver/painter, I certainly didn't come up with it on my own, but it works nicely.
Orange is a powerful color, so be careful adding very judiciously. And, while some hen mallards really tend toward the orange and others don't so much........ If you want the "typical" look most associate with hen mallards, it does need a little (very little) orange.......