"horse with brown and white patches," 1654, from skued "skewbald" (c.1440), of unknown origin, + bald "having white patches" (see bald). First element apparently unconnected with skew (v.); O.E.D. suggests perhaps from O.Fr. escu "shield," but also
notes a close resemblance in form and sense with Icel. skjottr, "the history of which is equally obscure."
"When the white is mixed with black it is called 'pie-bald,' with bay the name of 'skew-bald' is given to it." ["Youatt's 'The Horse,' " 1866]