Celie is challenged to learn to accept herself and to love herself in the story of the novel. One thing that helps her achieve this end is a new perspective of God (which extends to a new perspective on life).
Celie shifts her views regarding God when she and Shug have a conversation about how God does not have to be imagined as a man with a beard, but can be understood as existing in everything.
Shug tells Celie that the created world is meant to be enjoyed. That is part of experiencing God. Included in Shug's list of examples of things to be enjoyed is the color purple.
This point of view is empowering, especially when considered in contrast to Celie's former views.
Celie is no longer beholden to a patriarchal view of life, abstractly, just as she has liberated herself from a patriarchal home life for the first time. She is free to place herself in a position of importance in her perspective.
As she does this, she becomes self-accepting inwardly and, by all accounts, more beautiful outwardly.
The symbol of the color purple is woven into her clothing and her demeanor in the rest of the novel as Celie learns to enjoy life and to love herself.