This is an interesting question, as I can't find any particular symbolic use of the colour red in this impressive text. What I can find evidence for is the use of blood (which is obviously red) to indicate symbolically how characters are wounded and hurting even when they are not literally wounded and hurting. For example, consider when Liesel turns on the mayor's wife and refuses her kind offer of a book. Note how the mayor's wife responds to Liesel's words of refusal and rejection:
She was battered and beaten up, and not from smiling this time. LIesel could see it on her face. Blood leaked from her nose and licked at her lips. Here eys had blackened. Cuts had opened up and a series of wounds were rising to the surface of her skin. All from the words. From Liesel's words.
Blood therefore is used symbolically to indicate here the way in which Liesel's words wounded the mayor's wife and how they almost physically injured her through their harshness. Although this does not specifically refer to the colour red, the fact that wounds are mentioned and blood is referred to perhaps shows us how we can infer red is used to refer to wounding, violence and physical harm.