Was Sally a white or black woman?

From the text, we can infer that Sally is black. We are not told either way. All we know about Sally is that she lives with Linda's grandmother.

I tapped softly at the window of a room, occupied by a woman, who had lived in the house several years. I knew she was a faithful friend, and could be trusted with my secret. I tapped several times before she heard me. At last she raised the window, and I whispered, "Sally, I have run away.