How to revert background colors (visible when deleting a file, "Properties" -windows, regedit, etc.) of Windows 11 back to white, when changes caused after trying WindowBlinds?

I wanted to modify the look of my Windows 11 OS, initially trying free programs like OpenShell and StartAllBack. None of the free programs changed my taskbar, expect something called RetroBar (and OpenShell only added it's logo to the corner of the taskbar).

I tried WindowBlinds 11's 30-day trial and every theme I applied did change things like the title bars of programs and the colors of file explorer and task manager, etc. I would've liked that, but WindowBlinds didn't modify my taskbar at all. I even tried it by combining OpenShell, but it still didn't allow me to change the look of the taskbar. (later I found that changing the 'Start' -area to the left corner instead of center helped with some themes, while others didn't fit correctly on a 2-monitor setup with a 1440p main and 1080p second monitor.)

I ended up uninstalling OpenShell, WindowBlinds and all these UI-altering programs. I still noticed, that certain areas of Windows, like notification boxes when deleting a file from the Recycle Bin or the background color in registry editor had changed to a brown-ish color, when it should be white by default as it has always has been.

I Googled this and someone had recommended the "Purge" command to undo these changes by Stardock. I purged and rebooted, nothing happened. I reinstalled WindowBlinds, applied the default theme, then purged, rebooted and nothing happened...

So, I had a System Restore -point that was created when first installing OpenShell a few days earlier (I believe this was before I had installed or tried WindowBlinds). So I reverted Windows back to that point and nothing else had changed, expect that the background color in these different Windows -boxes was now blue (this was similar or the same color as the "accent color" that had been chosen in 'Settings > Personalization > Colors', although the option "Show accent colors on tile bars and windows borders" had been unchecked.)

As an example, let me just show you a basic picture of regedit from the internet. This is how my regedit looked like before.

As a reference, I just added the color change in Paint, explaining how my regedit looks like now:

It's not the correct color I'm seeing, but it's just an example. Also, in my reference pic there's an upper bar that has "Name", "Type" and "Data" in the colored area, which is actually still remained white.

When removing a file to Recycle Bin or deleting it from there, the notification area should look like this:


but instead it looks like this:

How should I fix this, is this even Stardocks/WindowBlinds fault, is there an easy fix for this or what?

Apparently, I still had WindowBlinds installed when I checked (I thought it was uninstalled after reverting to the System Restore -point) but I couldn't open it or uninstall it and the "Purge" command just said errors. So I re-installed WindowBlinds and effectively, whenever I chose the "Default" -theme, it's the same exact thing as now. Everything else is "default Windows", except these random background colors. I played around with a few different themes, just to see if WindowBlinds is somehow responsible or can affect a change to this issue, just to realize that every theme changed those random background colors to something that was in style of each theme.

So, Reinstalling WB, changing back to "Default" theme, doing the 'Purge' -prompt again and rebooting Windows didn't do anything once again.