In The Color Purple, Celie and Nettie's education, identities, roles as females, and families are all shaped by setting. Whereas Nettie escapes the abusive setting of Alphonso's house, Celie is victimized by it. Whereas Nettie is educated in school and at home by the missionary couple, Celie is continually abused by Alphonso, Mr.___, and Harpo. Whereas Nettie escapes the deep South and ventures to Africa, Celie remains a maid in her own house. All told, Celie is defined by a domestic setting, while Nettie is not.
It is not until Celie decides to leave Mr.___ and change her setting that she becomes a self-sufficient and courageous "womanist." Once she leaves Mr.___'s patriarchal and oppressive house, Celie achieves the American Dream by establishing her pants store.
The African subplot in Nettie's letters runs concurrent with Celie's decision to leave Mr.___: the more Celie reads about Nettie's African setting, the more courageous she becomes in changing her own. Celie realizes that she has been denied her African setting by Mr.___. The African setting is where her sister and children live; it is her "color purple," her royal garb, for she is a mother on two continents.
Ironically, the African setting is plagued by the same kind of patriarchal oppression of women as rural America. Tashi is limited to a domestic role in the tribe just as Celie is. Worse, Africa is being colonized by white colonial powers. So, Celie and Nettie are denied setting (heritage) by both black males in America and white males in Africa.
In the end, setting is the key to establishing a lasting female community, as Alphonso magically bequeaths his house to Celie, Nettie and the kids come home, and Shug and Sophia all move in to create a perfect maternal society.