@gary_sc Now there is a way 🙂 Well... more like an ugly hack. But it works. You have to use a hex editor though.
Here I've changed the border color to red, as a proof of concept - you can choose any color you want. Tested on Windows.

Locate `dvaui.dll` in your Bridge installation folder. Backup this file. Quit the Bridge app. Modify the file at your own risk!
Open a hex editor (for example https://hexed.it/ - works in a browser), load `dvaui.dll` and search for `spectrum-global-color-blue-400` text string.
Skip the first match. Then you will find that string in three more places:
"spectrum-global-color-blue-400": "rgb(52, 143, 244)" - for the "Dark" color theme
"spectrum-global-color-blue-400": "rgb(29, 128, 245)" - for the "Darkest " color theme
"spectrum-global-color-blue-400": "rgb(20, 122, 243)" - for the "Light" color theme
Simply change the RGB values to something you like. Be careful not to change the number of characters within the parentheses. For example, if you want to change the border color for the "Darkest " color theme to black, just add some spaces in place of the missing digits:
"spectrum-global-color-blue-400": "rgb(29, 128, 245)" - original
"spectrum-global-color-blue-400": "rgb( 0, 0, 0)" - modified
I found rgb(60, 60, 60) to my liking, for the darkest mode - it still shows the active panel but is not distracting at all.

Save the modified file on your desktop, rename the original file to `dvaui.dll.original`, and copy the modified file to the Bridge installation directory (requires admin rights). Make sure the modified file is named `dvaui.dll`.
Open Bridge. The annoying blue borders are gone! 🙂
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