Trying to install Kasa smart switch but having trouble with ground wire
Edit: switches (not receptacles) are allowed to make a ground connection via the mounting screws, even if the switch body doesn't rest hard against the metal  junction box.  So that solves that.  

Ground wires are always green, green/yellow, or bare copper, except in old installations in Russia.  Ground wires usually go onto green screws.  Use of stab connections for grounds is prohibited because of their unreliability.