In Hawthorne's The Scarlet Letter, he employs the use of color as symbol throughout the piece.
Beginning with the scarlet red of the A in the beginning, the red here represents evil and sin. Hester keeps her A throughout the book. As we get closer to the end and watch her, that red turns into a love for others.
As Pearl grows, she creates her own A:
As the last touch to her mermaid's garb, Pearl took some eel-grass, and imitated, as best she could, on her own bosom, the decoration with which she was so familiar... A letter, the letter A, - but freshly green, instead of scarlet.
This green A is in stark contrast to Hester's and it occurs as Pearl comes of age to ask what the scarlet letter means and recognizes it means the same as the minister's hand going over his heart.
The attached essay discusses in part the light and dark references.
Another aspect to consider might be just re-reading that first chapter again. It is rich with light and dark images, and it is worth considering the red on the flower right there.
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