Google Maps Api v3, custom Cluster icon

Google changed his repo. Latest cluster repo is: https://github.com/googlemaps/js-marker-clusterer images : https://github.com/googlemaps/js-marker-clusterer/tree/gh-pages/images

You may also consider downloading source and give link from your local path. This way you will have more control of resources your application needs.

local_path "/pucblic/"
mcOptions = {styles: [{
height: 53,
url: local_path+"m1.png",
width: 53
},
{
height: 56,
url: local_path+"m2.png",
width: 56
},
{
height: 66,
url: local_path+"m3.png",
width: 66
},
{
height: 78,
url: local_path+"m4.png",
width: 78
},
{
height: 90,
url:  local_path+"m5.png",
width: 90
}]}

A shortcut is overriding the image path like this:

MarkerClusterer.prototype.MARKER_CLUSTER_IMAGE_PATH_ = 
    "https://raw.githubusercontent.com/googlemaps/v3-utility-library/master/markerclustererplus/images/m";

You need to use styles parameter when initializing MarkerClusterer object - the code below shows default styles so if you want to recolour one of the icons just change the relevant url to your image...

//set style options for marker clusters (these are the default styles)
mcOptions = {styles: [{
height: 53,
url: "http://google-maps-utility-library-v3.googlecode.com/svn/trunk/markerclusterer/images/m1.png",
width: 53
},
{
height: 56,
url: "https://github.com/googlemaps/js-marker-clusterer/tree/gh-pages/images/m2.png",
width: 56
},
{
height: 66,
url: "https://github.com/googlemaps/js-marker-clusterer/tree/gh-pages/images/m3.png",
width: 66
},
{
height: 78,
url: "https://github.com/googlemaps/js-marker-clusterer/tree/gh-pages/images/m4.png",
width: 78
},
{
height: 90,
url: "https://github.com/googlemaps/js-marker-clusterer/tree/gh-pages/images/m5.png",
width: 90
}]}

//init clusterer with your options
var mc = new MarkerClusterer(map, markers, mcOptions);