Sentence:  The motifs of impersonal interdependence and insulation of residential communities have polarized ; the schism between central city and suburb , <WSD>Negro</WSD> and White , blue collar and white collar can be viewed as symptomatic of this deeper polarization of trends in the metropolis . 
Meaning of the word marked with <WSD> tags:  a person with dark skin who comes from Africa (or whose ancestors came from Africa)