In Blender’s weight paint mode, by default you can’t precisely see which area has zero weight paint.
For clearer visibility, turn on the options on 2nd screenshot while in weight paint mode.


Random notes
In Blender’s weight paint mode, by default you can’t precisely see which area has zero weight paint.
For clearer visibility, turn on the options on 2nd screenshot while in weight paint mode.
Preferences -> Get Extensions -> LoopTools