The Audubon Society Encyclopedia of  NORTH AMERICAN BIRDS  (  John K. Terres, 1980)   says....
 

A special and much debated kind of cryptic coloration has been called obliterate shading, or countershading.
Birds such as sand-pipers, plovers sparrows and others often have dark-colored backs and white underparts
The principle of countershading, first called to the attention of naturalist  by G. H. Thayer (1909) , functions as concealing in nature.