This book is neither a Thursday Next book, nor a Nursery Crimes book. It is set in a dystopia, where one's color perception determines one's place in society. I found it a more difficult secondary world to enter than either the Thursday Next books or the Nursery Crimes books, yet I found it quite thought-provoking, and in some ways a more serious work.
I was a bit disturbed by the fact that an immoral act by the main character at the end of the book was not more authorially condemned than it was.
I don't exactly recommend Fforde's books, because they're kind of bizarre, but I love them and am looking forward to reading the ones I haven't yet read (two others in the Shades of Grey series, and any in the Dragonslayers series, which I just learned about today).