Through no deliberate effort or plan, I have three books in my library with remarkably similar covers. That may not sound too interesting. Publishers often produce thematic collections with unified cover designs. Some topics, published by different companies, can have shared design traits as well. True-crime mass market paperbacks are almost always black with red accents. Books of the Nazis or Hitler are likewise black and red and you will need to look very carefully to find a book about Hitler that does not also have his recognizable mug on the cover.