To revive this thread: the well-known John Jacob Niles reworking of Black Is The Colour is of an Appalachian song in Sharp's collection, collected from Mrs Lizzie Roberts at Hot Springs, NC, published in Volume II [1921] of his "Folk-Songs of English Origin collected in the Appalachian Mountains". It was the words that Niles reworked: Mrs Roberts's tune was quite different, with none of Niles's rather embarrassingly 'poetic' repetitions of "Black" &c. It can be found on page 64 of Faber's misleadingly titled but very useful paperback compilation, "Eighty English Folk Songs", ed Maud Karpeles (1968, but still in print - I think!).