"Books? You want books?! Ha! We've got books on hairy otters, on onions and on mars! All the fungus you could care for, plus, three triple zillion stars. We've got books on flossing teeth, plus three books on tossing sheep. If we spent our lives just counting books, we'd never get to sleep!" -Leopold the Librarian ("The Great Wishy Woz")
The books getting darker comes along with (spoiler) Voldemort coming back. It just can't be helped.
Btw, I was looking at an interview with Ms. Rowling and she said
SCHOOL CHILDREN (all at once):
Do you believe in magic?
JK Rowling:
I'm sorry to say this, because often when I answer this question I get a groan but I don't believe in magic. I don't believe in it as it appears in the books. I could be slightly corny and say I believe in other kinds of magic. The magic of the imagination for example and love, but magic as in waving a magic wand and making things happen… no I don't. I'd love to be able to, but I'm afraid I can't.
