如何让Google Charts在散点图中显示多种颜色？

function drawChart() {
  var data = new google.visualization.DataTable();
  data.addColumn('number', 'X');
  data.addColumn('number', 'Y');
  data.addColumn({type:'string', role:'style'});
  data.addRows([
    [1, 1, 'color: red'],
    [2, 2, 'color: blue'],
    [3, 3, 'color: green'],
    [4, 4, 'color: yellow']
  ]);

  var options = {
    legend: 'none',
    colorAxis: {
      colors: ['red', 'blue', 'green', 'yellow']
    }
  };

  var chart = new google.visualization.ScatterChart(document.getElementById('chart_div'));
  chart.draw(data, options);
}