The characters seem realistic too. When the girls were children (in the early 50's) racial segregation was still pretty serious but being only 8 years old, color didn't bother the girls - child's innocence. But as they aged they realized the seriousness of the problem and it began to affect them, which is probably true for people growing up in the time of racial segregation.
The element in the story that appear most prominent and prevalent is when the girls witnessed Maggie (the kitchen help) getting beat up by the "gar girls." That event stuck with them the rest of their lives and effected how the girls saw one another as well as how they lived the rest of their lives. Roberta viewed Twyla as cruel and unchanging every time she saw her just because she imagined that Maggie was a black woman and they kicked her. This shows that Roberta may have been slightly racist because she wanted to see the black woman hurt. But her perception of what happened that day changes consistently with her mood. Twyla, on the other hand, thought that Maggie was a white woman and compares her to her own mother - empty, with no one home because she is deaf and her mother might as well be. This event in the girls lives molds well with the historical aspects of the time. Roberta was slightly racist (which is what segregation was all about), but so was Twyla. They both secretly wanted to see the other race hurt. Twyla was more subtle than Roberta because she didn't flat out say she wanted Maggie to be white and get hurt.