Celie and Albert are two great characters to look at regarding this question. Each of them love Shug Avery and have been changed by Shug - and thrown over by her. Both Celie and Albert are alone for a time (before Celie's children return with Nettie) and in this period they become friends. Such a change in their adversarial and abusive relationship constitutes solid evidence that a moral reassessment has taken place.
In this friendship Celie shows that she no longer needs to measure herself by other's estimations. She is her own person, so much so that she can let the past go (with all its beatings and dramas) and forgive.
This is an overtly spiritual change for Celie as her relationship to religion and spirituality have significantly changed, allowing her to realize herselfwithin the scope of spiritual thought. No longer is God a man with a white beard for her. This change of perspective proves to be the beginnings of wider changes in Celie's character as she moves toward a healthy self-concept.
Near the novel's end, when Celie and Albert have reconciled, Albert confesses his life's disappointment to Celie and his bafflement that things have turned out the way they have. He laments that everyone loves Shug Avery but only Shug lives him.
Celie tells him:
"If you know your heart sorry, I say, that mean it not quite as spoilt as you think."
For Albert, this admission of flaw and fault and weakness is indicative of the maturity his character has achieved. For Celie, her offer of acknowledgment - that he is not all bad - indicates her own great strides toward maturity, self-acceptance, and self-empowerment.
The struggles that Celie goes through over the course of the novel are each resolved in the end. She has been alienated from herself and from her children but overcomes both of these negative states in the end. She has been denied love, then finds love only to lose it again, but she comes to terms with love as a wholly positive and compassionate thing.
Early in the novel these positive positions were impossible for Celie. Her world view was forged entirely "in the negative". This all changes in the end.
As a poor, half-literate black woman, Celie lacks the apparatus for success and happiness. Her transfiguration into a joyful soul proves that redemption is possible for all people open to human kindness and love. (eNotes)
The end of The Color Purple effectively resolves all of the major conflicts, including spiritual and moral ones.
In Africa, Adam and Tashi discover a nearly-Utopian society in a canyon in Africa; it is a place where black men and women work together for the greater good and for societal harmony. To show his solidarity with Tashi, Adam scars his cheeks. Now, if they return to the United States, they will both be similarly "marked."
Celie, for her part, adjusts to life without Shug. Just as she has come to this place of acceptance, Shug returns. Self-acceptance was Celie's life lesson; when it is learned, she is rewarded.