CAGs help you to display buttons only under some circumstances 
For the background color, you'd have to work with apple script, but I'm not sure about how to toggle it from one button 
Changing it once wouldn't be a problem, but changing it back when it was activated could be difficult.
Maybe there are some possibilities with menu items again, but I don't know meet.google at all, so I can't help you with this Skype, TeamViewer etc don't present any problem regarding this, but as meet.google is basically just a website I'm stuck here…