Breeding males have black backs and white underparts. Their wings are black with a large white patch covering the secondary flight feathers and a large portion of the coverts. Their heads are predominantly black with iridescent green and purple highlights. A wide white patch extends from just behind the ears all the way to the back of the head. Their bills are blue-black in color.
Females are mostly dark brown on the back, head, and wings with paler gray underparts.
They have a small half-dome shaped patch of white feathers below the ear and a small white wing patch. The bill of the female is dark brown to black. All Buffleheads have dark brown eyes and pink legs and feet. Male Buffleheads in non-breeding plumage closely resemble the females but can be distinguished by their larger size, slightly larger cheek patch, and larger wing patch. Juveniles are grayish-brown with small indistinct cheek patches.