I need help with wiring a HS220 smart dimmer switch. I am installing an HS220 smart dimmer switch in the place of a regular wall switch. 

The switch I am removing has a black wire connected to common, a red wire connected to a brass screw, and a black wire connected to a brass screw (see photos below). 

The smart dimmer switch has a white wire, green wire, a red screw labeled load, and a black screw labeled line. The dimmer switch is a smart switch and requires a neutral wire (usually white), but, there is no white within the junction box. However, there is a bundle of gray wires. I think that the gray wires might be neutral, but, I'm not sure. 

Does anyone know how to properly connect the HS220 with the wiring I have?