Which psychological color principle is most commonly applied to thriller and horror book covers to signal the genre to potential readers?

Book cover design is a fascinating intersection of art and marketing psychology. Publishers invest heavily in cover designs that will capture attention and drive sales in increasingly competitive retail environments. This poll tests your knowledge about the psychological principles that influence book cover designs and their impact on consumer purchasing decisions in the literary marketplace. Do you know what makes readers pick up one book over another?

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The Von Restorff effect - using primarily red and black to create high contrast that signals danger
The Isolation effect - using primarily blue and green tones to create a sense of isolation and melancholy
The Zeigarnik effect - using yellow as the dominant color to create mental tension and incompleteness
The Baader-Meinhof phenomenon - using purple gradients to increase frequency illusion and memorability