reopening discussion: Custom background for Boards

It would be great, to have a customizable background for Boards.
By this I mean for example setting a custom background color for a board or even an image. I think this is a Feature, that Trello offers.
In my application it would help users to differentiate between Boards with similar topics. Having a custom background makes it easy to see, which Board you are working on.

Is your feature request related to a problem? Please describe.
Its not a problem, rather a UX improvement.

Describe the solution you'd like
A setting in the Board details which allows to set a custom background color or even lets the user upload or choose an image to be used (maybe blurred) as the background.

Describe alternatives you've considered
The only ability to mark boards with colors is the small circle next to the boards name, which is not very prominent...
I tried fiddling with some CSS, but that does not really work out, since it interferes with shadows and other graphic effects on the existing UI

Additional context
This is a duplicate of Issue #1051 which is already quite old and closed for being stale. I would like to open the discussion on this Feature again.

The issue names no files or tests; start by reviewing the Board details and board-list UI, then read the prior discussion in issue #1051. Define the supported customization scope before implementation, with completion requiring a usable board background setting that does not interfere with existing UI effects.