No matter how much the adage “Don’t judge a book by its cover” is trotted out, we all do it. It’s in our nature to make quick assumptions about things, especially when we have literally millions of books to choose from. It’s easy to make quick judgements based on book cover design.
Think about walking through your local bookstore or perusing your library’s shelves. You’re looking at spines, and only spines, most of the time. Then one book stands out. You pull it from the shelf and give the cover a read.
Why did you choose that book, in particular? Most likely, the color stood out to you.