Semantic colors are set of CSS to apply colorful theme to individual tiddlers for categorisation purpose.

https://kookma.github.io/TW-Semantic-Colors/

Tiddlywiki "semantic colors" has two objectives:

1. How it is simply possible to apply theme to an individual tiddler
2. Use semantic colors for categorisation

Some use cases

Learning materials (each topic, category can have dedicated semantic color, like learning a foreign language)

Slideshow (section divider, each part can have a semantic color)

Books and tutorials ( different semantic colors can be applied to chapters, specific subjects, like example tiddlers)

Visual tags (instead of looking for tag bar and see to what category this subject (tiddler) belongs, you can identify it by its semantic color)