Symbolism, Imagery, Allegory
At the end of the book, Sarah returns home after her solo wagon ride into town and shows the children what she bought: blue, green, and gray colored pencils. The pencils show the children that she's willing to give up her beloved sea in order to stay with them—and they also give Sarah a way to stay connected to the sea in her new home:
"Blue," said Caleb slowly, "and gray. And green."
Sarah nodded.
Suddenly Caleb grinned.
"Papa," he called. "Papa, come quickly! Sarah has brought the sea!" (9.57-60)
Sarah uses her colored pencils to draw pictures of the sea and post them around the house, filling their little house on the prairie with images of the sea. With that, Sarah keeps a bit of her first home alive in her new home.