Here's a thought -- if you think that there is a need to categorize your photos, use an app that includes things like keywording and maybe collections, so that you can with a click display all photos that have the keyword "monochrome" or "grayscale" or whatever. Plus, with online gallery software, use one that allows you to cross-post pics into different categories. For example, I use PBase and I can upload photos for a specific shoot but also "copy" that photo to a different gallery, such as a "grayscale" gallery. That way, I can access photos from more than one viewpoint.