You didn't render the rest of the picture to greyscale. Might have worked better with just one book yellow?. You have dozens of little bits of yellow sticking out in places you don't want to highlight and shades of green in places too. Good try, neat idea.
I like what ya were trying to do here (I think). If you were trying to isolate the dummie books, you should have used a different technique. The way you did it left yellow all over the shot. This makes it a little confusing. If you would have masked out all but the dummy books, it would make for a much cleaner composition and isn't too much more difficult.
TC
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