"The collier has a daughter" of great beauty. "A laird he was that sought her, Rich baith in lands and money." (She declares that she is too young and black to love a laird, and that she will have a man "the colour o' my daddie")
There are several early printed texts of this (reportedly Herd, Thomson, Johnson, etc.). Comparing the _Scots Musical Museum_ version with MacColl's version, I have to think they are recensionally different -- the _Museum_ version is a very flowery description of how the laird courts the girl, with no real ending; the MacColl text has her reject him.
I suspect the _Museum_ text is one of its rewrites (not by Burns), and a weak one. But it's possible that the folk process improved a weak song.
The tunes, apart from one measure in the middle, are note-for-note identical. - RBW