When melanin occurs in the cortex only, the feather is brown or gray. This is called foreground melanin. In dark black birds, such as crows and ravens, melanin is found in both the core and cortex. The relative concentrations of foreground melanin and core melanin control the color that we see. Thus, in this Hairy Woodpecker in the area of the wings that are brown, the relative concentration of foreground melanin is very high.
It should be noted that Hairy Woodpecker's colors vary greatly depending on the region they inhabit. Eastern birds are generally black and white. Pacific Northwest birds are brown and black. Hairy Woodpeckers in the interior west have nearly solid black wings. Birds in the highlands of eastern Costa Rica have cinnamon underparts.