Styling MarkerClusterer Icons?

I am using the MarkerCluster.js to create clustering in my google maps api. The clusters work how I want them however I want to style differently than yellow, blue and red circles. I was trying to use the MarkerStyleOptions and it says you have an array of styles with the smallest cluster icon first and the biggest last. I tried to create this below but I am getting really confused about what syntax to use and can't find any good examples.

var clusterStyles = [
    [opt_textColor: 'white'],
    [opt_textColor: 'white'],
    [opt_textColor: 'white']
];

var mcOptions = {
    gridSize: 50,
    styles: clusterStyles,
    maxZoom: 15
};
var markerclusterer = new MarkerClusterer(map, cluster, mcOptions);