Now there are several ways I can interpret this.
1. Favorite John GREEN book ;)
2. Favorite book about recycling (nahh...)
3. Favorite book with a green cover
I'm going to go with the last one
So my favorite GREEN book is....
Insurgent by Veronica Roth
See, it's green :)
For those of you who don't know, Insurgent is the second installment of the hugely successful Divergent Series.
If you haven't read it yet, go read it!