Which retail color-coding system, introduced in 2002, revolutionized the marketing of crime fiction books and became an industry standard for genre identification?

In the competitive world of book retail, publishers and bookstores are constantly innovating their marketing strategies to help titles stand out. Color psychology plays a significant role in book cover design and retail displays, influencing consumer perception and purchase decisions. Test your knowledge about a famous book retail marketing innovation that revolutionized how we identify literary genres at a glance.

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Penguin's orange spine system for classics
Black spine with red lettering for horror novels
Faber & Faber's blue covers for poetry collections
HarperCollins' 'blood splatter' black and red covers for crime fiction