The UK/USA spelling issue leads to quite a lot of problems in a database such as this. Sharp, being English, used the standard English spelling of colour when he noted the song; it was published as such here. Evidently the American publication used the American spelling. In the main, the difficulty works in the opposite direction; people post songs here that were noted and published in Britain or Ireland but change the spelling of words to the American forms. As a rule, the spelling used in the published source should be retained, wherever it comes from.

In this particular case, of course, the spelling difference is more than usually liable to lead to confusion, and I, too, forgot that there were two separate, differently spelled sets in the DT when Dicho asked about it in another thread, recently revived by a visitor who had failed to find this, more substantive one. If only people would stick to one discussion on any particular song, we could avoid a lot of unnecessary duplication and confusion.

Black is the Colo[u]r is number 3103 in the Roud Folk Song Index; all entries so far relate to American examples, except for two sets from Sean 'ac Donncha and Joe Heaney, both dating from the early 1970s (though presumably in their repertoires earlier than that). Whether or not this indicates an Irish origin for either song or tune remains to be seen, as does whether or not there is a significant connection between this and the Sailors's/Soldier's Life group (Roud 273, Laws K12); as I mentioned earlier, I think that the latter question merits further investigation, but a direct connection should not yet be taken as read.

The former question would in large degree depend on deeper investigation of the latter; that song having been found far more widely in tradition in the USA, England, Scotland, Ireland, and Canada (roughly in order of frequency). In particular, examination of correpondences between the recorded tunes might be helpful.