There is one poem called “Cape Coloured Batman”. I’m finding references to it, but not the full text.
That’s odd - for me, the link goes to the Google Books preview that has the full poem (it’s not that long).
But perhaps a few lines will prove illustrative:
“This is the man the Empires made
From lesser breeds, the child of Trade
Left without hope in History’s shade;
Shouldered aside into any old place,
Damned from birth by the great disgrace,
A touch of the tar-brush in his face”
It’s a poem about Butler finding his batman drunk under a tree:
Nelson, my batman, the bastard, drunk.
Note that bastard here isn’t an ordinary pejorative, but a racist epithet.