Download attached and drag into some TiddlyWiki ( TiddlyWiki.com !) to play.
So I dreamt up a scenario in which tiddlers tagged as Student get a particular when in view mode, but do go back to plain white when in edit mode.
And then I decided to build a basic interface to pick the color via the "Student" tag's related tiddler.
And then decided to make that "Student" tag's related tiddler a bit of a documentation tiddler by displaying the relevant CSS "right there" in an edit text widget that is disabled and 100% wide via a css class.
Good fun !