"Bit by bit, however, urban whites carved a color line through the city."

The inciting incident in Arc of Justice is a mob attack on Ossian Sweet's    home, just one of the ways in which urban whites in cities across America, like Detroit, respond to the influx and upward mobility of black migrants.   Often, forms of color line enforcement are not legally sanctioned, but nor are they often prosecuted.

"And everyone knew that when the color line was breached, housing values would collapse, spinning downward until Garland Avenue was swallowed into the ghetto and everything was lost." 

This quote encapsulates the snowball-effect fear that many urban whites  have about sharing their neighborhoods with black residents. Real estate  agents fan the flames of these fears by lowering home values after a black     person buys a home in an all-white neighborhood.

"Other men might have hated to see their youth slipping from them." 

One step closer to his goal of moving among an urban elite, Ossian cultivates an air of maturity and professionalism beginning in his medical training atHoward. This cultivation is also a reaction to the way in which all black men, regardless of age or status, are, in the South, regarded as 'boys.'