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!
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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.
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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.

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Let me know if you need any help!