Manila is a Finder extension that lets you change the colors of your folders from the context menu.
As the author seems to be inactive now, I forked this great project to add localizations (German for now). I also added a dark blue icon colour and moved the default blue to the top of the menu list for an easier "reset back to original".
Requires macOS 12.1 or later.
This fork requires you to build the Extension yourself in Xcode (sorry, I can't provide binaries atm).
After cloning or downloading the source, you need to change the app's PRODUCT_BUNDLE_IDENTIFIER, CODE_SIGN_IDENTITY and DEVELOPMENT_TEAM to your personal apple dev account settings.
For macOS 12 you need to manually enable the extension in System Preferences > Extensions > Finder Extensions.
For macOS 13 this is now in System Preferences > Privacy & Security > Extensions > Added Extensions / Finder Extensions. You also need to allow access to Desktop and Documents folders in System Preferences > Privacy & Security > Files & Folders.
Right click on one or more folders whose color you want to change, go to the Color menu, and pick a color.