Thanks for this thread - my questions are continual ...
One thing I'm wondering about atm is the newer ApplicationWallpaper.qml. I previously could edit this file pretty easily to customize the bg of apps by just changing "...(0, 0, 0, .65)" line to whatever rgb and opacity values I want. Now, (starting with 3.0, I think), the opacity value still applies as expected, but the color values don't. It seems like it's only black, no matter what rgb values you enter. I figured it has something to do with the other info in the file, (like "effect: "glass" overlayColor: Theme.colorScheme === Theme.DarkOnLight", etc), but I have tweaked with no results. I also get the sense that the ApplicationWindow file plays a role, but it's a bigger file, and can't tell what most of it is referring to...