“I started to think that NC-17 movies perhaps shared a common visual string in their marketing materials  dark and provocative… I started with R and pulled up the top five movies’ posters. Less provocative but very dark. I moved on to PG-13’s five. Not provocative at all but dark nonetheless. PG’s five? Much friendlier but, yes, dark. It wasn’t until I got to the five Gs that I started seeing some bright colors in the movie posters.” (Thanks HOW Blog!)