I only heard of this song relatively recently, and liked it pretty well from the very first, but the "skin black as coal" line gave me pause enough to reject the idea of learning to sing and play it myself.

I figured that, in the context of Dublin, it didn't mean much more than that the rival lover was not only a student, but very obviously a foreigner. In the US, on the other hand, there's a whole lot more "baggage" involved.