"of two different colors, having spots or patches of white and black or another color," 1580s, formed from pie (n.2) "magpie" + bald in its older sense of "spotted, white;" in reference to the black-and-white plumage of the magpie. Hence, "of mixed character, heterogeneous, mongrel" (1580s). Properly only of black-and-white colorings (compare skewbald).