This is a set of CSS to apply colorful theme to individual tiddlers for categorization purpose. One main use case is learning area. For example you can use different colors for different levels of learning like orange for beginners and blue for advanced learners.
It is possible to define different categories like (basics, macros, widgets) and customize the classes for that purpose. For example all tiddlers tagged with macro uses class Clay and all tiddlers tagged with widget uses class Yale.