In 1935, which innovative marketing strategy did Penguin Books pioneer that revolutionized the publishing industry?

In the world of publishing, certain brands have become iconic symbols of literature itself. Penguin Books revolutionized reading culture by making quality literature affordable and accessible to the masses. This trivia question explores the fascinating brand history behind one of publishing's most recognizable logos and how it transformed the literary landscape of the 20th century.

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Color-coded book covers to indicate different genres (orange for fiction, blue for biography, etc.)
The first subscription-based book club with monthly home deliveries
First publisher to include author photographs on all book covers
Introduction of the first hardcover-paperback simultaneous release model