User should be able to select a different color for the background at runtime (via the tab context menu?)

### Right clicking on the tab windows to change color only changes color for the tab itself.
Not the tab window background as claimed in your documentation here: https://docs.microsoft.com/en-us/windows/terminal/tips-and-tricks#color-a-tab

Start by reproducing the behavior from the tab context menu and compare it with the linked color-a-tab documentation. Trace how the selected color is applied to the tab and determine the corresponding tab-window background behavior; done means the runtime selection changes the background as documented.

Written by the indexing model from the issue text.