The current vibrance does not reset to the value selected at "Windows Vibrance Level" when you exit VibranceGUI while having an Program/Game open that you have selected to use VibranceGUI with.
Reproduce example:
Affect Primary Monitor only" is set.
VibranceGUI is on another Monitor
Program to trigger vibrance change on is located on primary monitor and has the current focus.
Vibrance changed.
Close Program -> Vibrance does not reset.
Resetting the computer fully also does not reset the vibrance back to default values.