Change map marker color when listing is clicked

gistfile1.txt

Map.prototype.toggleMarkerColor = function(listingId){ // this is not running
	alert("The map heard the click event!"); 
	var idx = this.markerMap[listingId];
	this.geoJson[idx].properties["marker-color"] = "#ffffff";
	this.markerLayer.setGeoJson(this.geoJson);
	this.markerLayer.addTo(this.map);
};

// Under Listings view...

$("li.listing-link").on('click', function(){ 
	var listingId = $(this).data('id');
	Map.toggleMarkerColor(listingId);	// Uncaught TypeError: undefined is not a function
});