A solid color? That's somewhat easy to simulate. Add a color source to your scene and position it just below the camera source. With "below" I mean it should be listed below the camera source in the list of sources. Then resize it so that it occupies exactly the same space as the camera source. Done. If the camera is inactive, it is transparent and the color shines through. If the camera is active, it replaces the camera.
If you need the camera in multiple scenes and need to arrange both sources in multiple scenes, create a group with both sources and add this group to your scene instead of both separately.
To make sources exactly the same size and position, right-click the source->Transform->Edit Transform. Here you can read and set position and size by pixel.