Which publisher pioneered the 'rainbow spine' redesign strategy in 2016, creating a collectible visual effect when their books were shelved together, leading to a 70% sales increase?

In the publishing world, book packaging and design have evolved dramatically to capture reader attention in an increasingly digital marketplace. From innovative dust jackets to special edition boxed sets, publishers have experimented with numerous packaging innovations to make physical books more desirable as collectible objects. This trivia question focuses on a groundbreaking packaging innovation that transformed a particular literary brand's market presence and sales strategy.

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Penguin Classics with their redesigned philosophy series
HarperCollins with their redesigned C.S. Lewis collection
Bloomsbury with their adult redesign of Harry Potter novels
Simon & Schuster with their redesigned Stephen King backlist