Is it a Mallard duck? A way to figure this out is if the duck has the colors yellow and brown as a baby. It will be all brown with yellow stripes all over it. The female baby mallard ducks tend to be only brown though. When your ducks get older and you are wondering if they are Mallard ducks the males will have the colors black, blue, yellow, and green. The female ducks tend to be brown and white.