I said there were a couple of points to clear up; here's the other one.

Just in case anyone's as confused as I was about the relationship between the Lizzie Roberts recording, the Niles version and the various renditions by Irish singers, here's John Jacob Niles' version
And here's Christie Moore's version

What Christie is singing is very close to the Lizzie Roberts version, and the same goes for the Corrs, Sinead O'Connor, Cara Dillon and so on. Whereas if you look up the Joan Baez recording, she sang the Niles composition (and I reckon it's sufficiently different from the traditional one to be called 'a composition'). Someone further up the thread suggested that Willie Clancy popularised the song in Ireland, having learned it from Jean Ritchie, and Jean herself said that she'd learned it from her sisters who had been at Berea college, and most probably learned the Cecil Sharp / Lizzie Roberts version there.

So there we have it: Lizzie Roberts' 'Black is the Colour', collected in Hot Springs, Madison County, North Carolina, has joined 'The Wild Rover' and 'Dirty Old Town' as another 'Honorary Irish' song. It's probably been obvious to everyone else for years, but I thought I'd share it anyway.