In modern slang, what does the word "spade" mean?

It's not modern slang. It's been around a long time. It exactly means, "n*gger," for it is just as derogatory. Even the idiom, "To call a spade a spade," skirts this definition with its synonym idiom, "Calling the kettle black." While the latter has nothing to do with race, the former intentional does by piggybacking the slang term onto an allusion to the latter.