You can control the color and opacity of the background behind cropped media, allowing for different backgrounds for each and every scene with cropped assets!
To change the background color and opacity of a scene with cropped media, click a scene to access 'Scene View'.
Then, click on 'Cropped Background Color' in the media editing toolbar.
Note: if a media asset is not cropped in a scene, this button will not appear.
From here, you can alter the color and opacity in the areas of the scene that are not filled by your media asset.
Let me know if you need any help!