The main UI supports the macOS' toggled light/dark modes, introduced in macOS 10.14 (Mojave).
New documents created in OS Dark mode will default to using a use a dark Tinderbox built-in colour scheme 'Dark Coral'. The default colour scheme for documents created in OS Light Mode is the built-in scheme 'Modern'.
These built-in schemes are listed on, and can applied via, the Colors tab of Document Settings (Edit menu or [Cmd]+8 shortcut)
If it is desired to have a 'light' general background to the view pane and $Text area whilst in OS Dark Mode, apply the 'Tinderbox 7' scheme. The KA table and general screen 'chrome' (tabs, etc.) of the app will remain dark but these two key parts of the window will take a light-on-dark colour style.
Likewise, if opening documents that were made in older OS versions or older Tinderbox versions and the colours look wrong, simply apply 'Tinderbox 7'. This will update the document's colour scheme to reflect the additional colour setting changes affected by OS Dark/Light mode.
When changing to dark mode or light mode with Tinderbox open, the text colour of the tabs is updated immediately.