White borders are back in 1.17

This problem is back in v1.17, I guess due to the recent changes around theming. The grey border is there to start with until you switch to another window and back (presumably it's part of the dark theme and doesn't get repainted until switching). Once you switch back it is white and will stay so even after closing/re-opening.

Steps to reproduce:

• Delete settings.json and state.json
• Open Terminal and switch to light theme
• Border is grey
• Alt tab to another window then back again
• Border is now forever white

Originally posted by @harristom in https://github.com/microsoft/terminal/issues/6620#issuecomment-1406570765