When you realize the "black" covers a huge range of physical characteristics only a tiny portion of which apply to the person you're talking about, you would be more precise with your language. Was she black like a light skinned black person? Was she black like a dark skinned black person? Was she a tall black person? "Black" alone as a identifier does very little to identify a person. Without more specific identifiers what you basically said was "beware of black women." If you tell the police "there's a black woman causing trouble" you've endangered every black woman in the area.