Currently, we have a lot of colorscheme colors. We don't even use all of them. The ones that we do use aren't always used in a consistent or even logical manner.
Examples of illogical and inconsistent usage:
* The button and menu item focus color is actually controlled by the View Focus Decoration color
* The Task Manager highlight color is controlled by the Button Focus Decoration color.
* `QPalette::Highlight` is mapped to Selection Background and is used somewhat interchangeably with Focus Decoration colors. This works fine for the current version of breeze, but not for any color scheme that uses a different Selection Background color from the Focus Decoration color.
* View NegativeText is used for MDI widget titlebars instead of Button NegativeText.
NOTE: I am looking for usage in the Breeze QStyle, QQC2/Kirigami, Breeze icons and the Breeze Plasma desktop theme.
Unused colors:
* Window: Alternate Background, Focus Decoration, Hover Decoration
* Button: Alternate Background
* Selection: Alternate Background, Focus Decoration, Hover Decoration
* Tooltip: Alternate Background, Focus Decoration, Hover Decoration
* Complementary: Most of these aren't used, but this is because it's uncommon to use an alternative colorscheme for some parts of the UI.
Possibly unused colors:
* I don't know for sure, but I would assume that all text colors are used.