no window frame transp. at all, and the slider only effects transp. of the space around expoler address bars, NOT of the window frames.
[EDIT]: loaded Diamond in SkinStudio, went to "Edit Titlebars and WindowFrames", "Edit UIS2 frames", "Extra Settings":
- enabled "use Aero Style Frames" --> the skin looks again as it used to.
I also changed "Aero frame colour alpha" to 50 and "Aero Frame Color" to 0, 62, 37 - looks much cooler and more pleasant now .. 
[EDIT2]: above is NOT a solution, because switching to Win Aero deactivates the title-bar effects like 'stay on-top on double-click' etc. I uninstalled the 7.19a Beta, rebooted, installed 7.10, and now everything is again the way it is supposed.
QUESTION: where in the skin (SkinStudio or manually in the uis, I don't care) do I change what in Aero is called "Border Padding": Vista or 7, Windows Color and Appearance, Border Padding. I changed it there from 4 to 1, but would like to know where that setting is in the Diamond WB skin. Or do I HAVE to do in Windows once I enabled Aero Style Frames in a skin?