Blue?! No, seriously, I think the colour blue has to be a significant feature of any powerpoint background for a presentation on this excellent novel. #2 makes a very good point concerning the need to signal that there is something not quite right about the situation that Kira finds herself in. You also might like to think of the way in which the world in which Kira lives is depicted as being brutal and savage, as shown by the way that her mother had to fight to keep Kira from being left to die as a baby. So, something mysterious and/or something that reflects the danger of this world would be good places to start.
How about a blue beach and ocean scene with the backlit figure of a young woman, silhouetted against the sky and ocean, with her arms raised to the sky as though gathering the blue. Too specific? How about just a blue dawn picture of ocean, sky and sand?
I'd do something dark and mysterious looking. The reason I would pick that would be to sort of remind people of the forest and how mysterious and scary it is. It could also evoke the general feeling that we get in this story that something is just not right, that something weird is going on under the surface. So I would pick whatever background seemed mysterious-looking to me.