This reminds me of the way Peter Rabbit is structured. The ending of the story suggests that there is a 'message' (in this case, something like 'just be patient and the green spring will come'). But the entire arc of the story, all the memory and the interesting things that happen, happens in the middle. So all things considered, this is a book about brown (not much about spring at all). So fun!
There's a wonderful double page spread with a cross section of everything that's happening underground, with the words "and the brown, still brown, has a greenish hum that you can only hear if you put your ear to the ground and close your eyes." I enjoy Erin Stead's illustration style even more in this one than in her Caldecott winner from before. And Fogliano's prose poem is very good. It's governed by a rhythm and a child's voice that reminded me of Ruth Krauss' A Hole is to Dig, which came right from kids.