Dialog scrim color on dark theme

Dialogs as a scrim to the background to emphasize the modal trait of dialogs. That scrim is a half-transparent black on the light theme. See below for the effect that has, greying out the activity in the background. I believe for a dark theme that scrim should be a transparent white (because a tranparent black doesn't have the same effect on a black background):

We had the same thing with the desktop dialogs and we solved it like described above there, here's what it looks like then:

Back then @ialokim found the description on the Material guide: briar-desktop!105 (comment 60781)

I have to say the guide is unfortunately not 100% clear, as often, so it's not clear whether that is an example or the spec. Also it doesn't give examples for dark theme.