This theme color applies to the tab title text of the statusbar tab that
is currently shown.
The (somewhat confusingly named) `statusbar.active` theme color now
applies to all other tabs (before, it applied to all tabs).
Coloring of a tab that is highlighted/has new messages is done as before
using the `statusbar.new` theme color.
The default color is set to `cyan`, and thus causes no visible change
for users -- until modified.