Folder Marker is a handy shell extension that enables you to quickly change folder icons to indicate a priority level or project status (high, low, done, half-done, planned etc.), or you can use it to mark a folder with a special icon or color of your choice.
Simply right-click on any folder and select the icon or color to be used from the newly added menu option. Folder Marker supports single and multiple folder selections and is freeware.