We use the term foil in literature to describe a character whose different qualities help us understand another character through contrast. The phrase comes from the way precious gems would have a thin polished foil placed behind them to help bring out the light in the gem. In the novel Claudia's feisty and resistant nature is in contrast to Pecola's passive victim. She draws our attention to her friend's suffering and to the wider social problems that allow it to happen. Also, Claudia's tough but strong family background allows her to survive the same pressures whilst Pecola's broken home and dysfunctional family lead her to ruin.
Through the story Claudia is the opposite of Pecola. This allows the reader to gain a deeper understanding of Pecola’s character through the contrast of the two.