Changes from the actual sway

Change colors for individual windows

*client.<class>* [global|default] <border> <background> <text> [<indicator> [<child_border>]]

• Nothing for per-window colors
• global for all windows
• default to remove any window specific colors

Reminder for myself : this is not a "rule", it is a client command. So if the window doesn't respect the criteria, it won't return to the default colors.