The current OOUI/M101 button design has "active" (on an otherwise un-flagged button) as a dark grey, which feels a bit too negative/disabled to me. Indeed, it's not clear to me that distinguishing between the current disabled and stylings is accessibility-compliant.
Proposed with overhauled color palette:
After T107953: Use progressive for selected states in OOUI toolbars shows the way with toolbars, maybe use of colour to show selected state more generally is for what we should aim?