What is the mood in the book Number the Stars by Lois Lowry?

Gathering Blue makes a lot more sense if you've also read The Giver. Both books are about an oppressive government in a dystopian society, although I feel that The Giver explains and shows this more fully.

Gathering Blue's theme, per se, is basically coming of age, and loss. The book's main character, Kira, loses her mother at the beginning of the novel, and over the course of the story, comes of age to become the newest seamstress. While she's stitching, she discovers that there is no blue thread. I think that the theme of 'blue' here, is actually an abstract concept, representing something we've lost and can't quite remember. Which, in turn, I think is a metaphor for freedom and/or childhood.