As a way to incorporate books into the activity, I decided to set up a book color scavenger hunt.
I set out a big pile of books...
What Color Is Your Underwear?, and ignored the other books. We found every color in that single book, so emptying your bookshelf onto the floor is entirely optional. You could just pick one or two books and go from there. (That way it's also portable. You could do this in the car or the waiting room.)