White: The Light and Purity Symbol

 The Cottonwood seeds that were floating in a blizzard in June and Cassia and the other people on the air train saw were white. 

In positive aspects, white is light, purity, innocence, and timelessness. I think this is how Molly feels about the Cottonwood seeds because the cottonwoods are one of her favorite trees.

In the negative aspects, white is death, terror, the supernatural, and the blinding truth. 

I think, in the big scheme of the story, the seeds were more like this, and used as foreshadowing, especially with the blinding truth part and how it would come to play a pivotal roll and theme in the story.