With macOS Big Sur I use colorful folders, for example yellowish dark for Documents, green for downloads, a tint of red for Music and so on. They all have a badge identifying its contents. I've been doing it since Mojave, keeping the same default style, just using new colors.
With OS9 though, having a badge in a folder icon helps a lot to identify its contents. I am a front-end web designer, UI/UX designer, and seeing so many purple folders without any idea of their content is madness. I just finished redoing some folder icons I've found, like the Games folder and Wallpaper (should be Pictures, actually) folder. And I created new icons for Multimedia folder and Downloads folder. I need to reorganize my collection of Icons that I have just started to collect around the web, a few weeks ago.
I'll release the customized ones as soon as I test them on OS 9 later. I made them using PS 2020 on Big Sur because I have a workflow that already works insanely fast. Just took me less than a hour to make them (could have made them in minutes if I hadn't wasted my time searching for an idea for a Multimedia folder badge. I ended using a play icon along with a film icon and IMO looks great).