Reproduction steps:
1. Open the attached project “BlackToolbar”
2. Select Scene view
3. In the Hierarchy window select “Main Camera” GameObject
4. Observe the toolbar of the Scene view
Expected result: The toolbar within the Scene view is visible
Actual result: The toolbar within the Scene view is black
Reproducible with: 2022.2.10f1, 2023.1.0b7, 2023.2.0a6
Couldn't test with: 2020.3.46f1, 2021.3.21f1 (user script errors)
Reproducible on: Windows 10
Note: Sometimes while moving the camera in the Scene view by right click, holding and dragging, the toolbar flickers