Which publishing company created the distinctive color-coded 'Penguin Classics' design system that revolutionized paperback branding and remains iconic today?

The publishing industry has seen remarkable transformations in how literature is marketed and branded. Major publishing houses have developed distinctive strategies to make certain book series instantly recognizable to consumers. This trivia question explores one of the most successful brand identity campaigns in modern literature that revolutionized how books are marketed to young adult and adult readers alike.

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Penguin Books (founded by Allen Lane)
Random House (founded by Bennett Cerf)
HarperCollins (founded as Harper & Brothers)
Simon & Schuster (founded by Richard Simon and Max Schuster)