What are the motifs in Bluish by Virginia Hamilton?

A crucial scene in the novel comes with the fourth part of Dreenie's Journal, in which the class visits the vivarium, or butterfly sanctuary. There, Dreenie and Bluish share an encounter with a Blue Morpho butterfly, a huge exotic butterfly with bright blue wings. The Blue Morpho alights on Bluish's arm, and she is amazed and touched by the sight of it. Max the student aide explains that butterflies with such exotic colorings are often toxic, and this causes Bluish's mood to fall swiftly, as she relates the butterfly's toxicity with her own battle with cancer.