Blue eyes seem to symbolize the cultural beauty and cachet attributed to whiteness in America. Different characters respond to blue eyes in different ways. Claudia, for example, resents the blue eyes of her white dolls, viewing their association with beauty ironically and with disdain. For Pecola, however, blue eyes are something to strive for. She believes that having blue eyes would change the way other people see her, giving her something white America values as beautiful. Even more interestingly, she believes she would see things differently through blue eyes, that they would somehow give her the relatively carefree life of a white, middle-class child.
In part because of her low self-esteem as a poor black child, Pecola does not believe in her own beauty or her own free will. She spends her life praying for a miracle because she cannot conceive of being able to change her life on her own.
We also like the idea that "blue" can refer to sadness. When Pecola believes she has acquired blue eyes at the end of the novel, we might understand her as actually having the saddest eyes of anyone in the novel.