The Spanish word for Black (both color and people) is "Negro" (Masculine singular) "Negra" (F/S) ("Negros" and "Negras" in plural). It's generally not used as a slur when reffering to real African People, but sometimes IS a slur aimed at darker skinned white people here (not in the media, since it's illegal).
As I said before, any word written in a different language than the rest of the text sounds as a slur, no matter what.
I oppose all sorts of slurs and racism and don't endorse it, but if you want to use Spanish I don't mind. There is not such a thing as anti-Hispanism in the world. Nobody will say Spanish speaking people are all racist.
But disgracefully there is something called anti-Semitism, and those anti-Semites are eager to quote anything they find on the web against the Jews and the Yiddish speaking martyrs.
So, I'd like you not be or look like racist, but if you will do so, then better in Spanish, and not in Yiddish