The whole thing is bizarre that it still goes on.
It's a song I did sing when I was younger, hadn't really thought about it, was just a song at the football, black was just widly used slang for dirty in that part of the world (there was also a term 'black afronted' that I never understood because they were just meaning 'afronted' the addition of the word black serves no purpose). When I did realise the perception of the song naturally I stopped/skipped that bit/muttered something else, none of that excuses the use of the word black, especially on that context (suggesting black = dirty) regardless of any aincient stories of coal mines, but you don't realise it's wrong until either the point it clicks or someone points it out. The fact it has been pointed out and continues at both Ayr games and Kilmarnock games (they seem to escape criticism for singing the same song) is frustrating.
I don't know how to make the point to people (and I've tried) that just because your intentions aren't racist that doesn't make it ok, a black player coming to Somerset/Rugby Park to play and hearing folk shouting about chasing black b*****ds is horrific. I'm amazed I've never heard a footballer talk about it before and it might help rid us of it if one did.