This is from the DU book.... I can't seem to find any decent pictures on google.... the drakes basically just look a lot like the hens do in the summer and very early fall. In the next few weeks, you'll start to see all the males brighten up with color.... some have already done so. Wood ducks (AKA summer ducks) already have fairly distinct color markings. mallards tend to get theirs pretty quick too.... and you'll already see some green on the heads.
Here is a decent size comparison between a mallard and a teal.