The tiddler colour cascade is a cascade used to choose which colour should be used for a particular tiddler tag and icon.

Core tiddler colour cascades can be found in $:/core/macros/tag, $:/core/ui/Components/tag-link, $:/core/ui/EditTemplate/tags, $:/core/ui/TagPickerTagTemplate, $:/core/ui/TagTemplate and $:/core/ui/ViewTemplate/title

The default tiddler tag colour cascade consists of:

1. If the tiddler has a color field, use the value as the colour for the tag-pill and the tiddler-icon
2. If the tiddler $:/config/DefaultTiddlerColour exists, use the value as the colour

You can see the current settings for the tiddler colour cascade in $:/ControlPanel under the Info -> Advanced -> Cascades -> Tiddler Colour tab.