d3js | circles update with force layout

based of this really nice example: pusher.com/dynamic-graphs-with-d3-js/

data generated in this format, looping over red, green, blue and incrementing the id:

render([{
    id: 1,
    color: 'red'
}, {
    id: 2,
    color: 'green'
}, {
    id: 3,
    color: 'blue'
}]);