Hello!
I was looking for solution to change color for window title bar.
For that I trying to edit file decoration.svg for current downloaded "window decoration" in Inkscape app (~/.local/share/aurorae/themes/). But it did not worked, color was the same (even after restart). But when I copy decoration.svg from other theme, it worked out. How does this work?
Later I try to return to default breeze theme (by theme I mean window decoration), but it was not breeze. For some reason it was like other theme.
But I didn't touch default breeze, I don't even know path to it location. I tried to delete that one theme thet was copied by breeze.
It worked out, but not how I expected: breeze now looks like another theme that was available.
https://i.imgur.com/xVW5ZiZ.png

It's really getting me nervous. How does this thing work? It's complete mess! Please, help.

I am running on KDE Neon based on 18.04 Ubuntu. Currently version of KDE Plasma - 5.19.4

Yes, the color looks darker in the middle area of the title bar.
I change colors like this:
Start -> Applications -> Settings -> System Settings
Colors -> Set it to Breeze
They no longer have the Edit button.
You have to hover your mouse over the giant Breeze icon.
At the bottom right of the giant Breeze, there is a pencil icon. Click it.
A window pops up.
Find Active Titlebar
Click the color thing and set
red=85
green=0
blue=255
Click OK
Find Inactive Titlebar
Click the color thing and set
red=80
green=80
blue=85
Click OK
Click Save As and give a name like Breeze2
Click Close
A new giant icon will appear called Breeze2. Click on it and at the bottom right, click on Apply.