While all PAGES and POSTS are blank by default, your special webpages (Home, Categories, Archives, About, and Pages) have certain default settings. These are easily changed—just select them, run the stamp, and add or subtract the desired background triggers.

Category notes have their $blogBkgOpt set to BKG-TEXTURE and CARD. As a result, their teasers appear as floatings cards atop the static and repeating BodyTexture.png of the current Theme Folder. The presence of the texture is a good indicator that you are looking at a category rather than a proper post (a POST or PAGE).