E. Cobham Brewer 18101897. Dictionary of Phrase and Fable. 1898.
Party-coloured. A corruption of pie-balled, speckled like a pie. The words Ball, Dun, and Favel are frequently given as names to cows. Ball means the cow with a mark on its face; Dun means the cow of a dun or brownish-yellow colour; and Favel means the bay cow. (Ball, in Gaelic, means a mark; ballach, speckled.)