One of my favourite things about having studied a creative subject is that now I am way more visually aware of patterns and trends in everyday life. Book covers are a great example, the design within genres are often similar giving visual clues to potential readers as to what the book is about.
Above there are just a small selection of Thrillers that feature a black background with white and an accent colour. To my mind the black represents the mysterious unknown of where the story will take you, the white gives great contrast and legibility, finally the pop of bright colour shows the unexpected turns within the book and helps to stand out on the shelf... or Amazon page!