Thank you, one and all. McGrath, I'm afraid Mr Leeder is right, I've seen this in at least two folk publications. I'd bet a nickel that the black/white context is probably the origin.
I thought that I'd reasoned out the definition correctly from its context, but I've made a few spectacular mistakes doing that. The best one came from reading a folktale as a child, about a man seeing a mermaid. "She wore no clothes, and even her long hair could not conceal her comeliness."For twenty years I thought "comely" meant "naked".