This could be an easy win, because besides offering something "trendy", we would also have an example in core of how subtheming works.
It may be so that this could even be as simple as implementing Color module support for Seven, and then making it a color scheme that people can select and tweak.
Related: https://github.com/backdrop/backdrop-issues/issues/4778
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VIEWS_STORAGE_OVERRIDE
Thanks Alejandro. That was the clues I needed.
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