Changing Circle fillColor in google maps api

Hi so I have created button which is creating a Circle on a Google map.

 this.Circle = new google.maps.Circle({
    strokeColor: '#FF0000',
    strokeOpacity: 0.8,
    strokeWeight: 2,
    fillColor: '#FF0000',
    fillOpacity: 0.35,
    radius: 100,
    editable: true,
      draggable: true

I would like to set typz() so it would be changing color of the circle to black.


How to do this?

Thanks for help!

What plugin is in use here?