chart color change Google Charts API

I'm using Google Charts API and I don't find in documentation how to change chart color foreground from black in white

this is the code:

      google.charts.load('current', {'packages':['corechart']});
  google.charts.setOnLoadCallback(drawChart);

  function drawChart() {
    var data = google.visualization.arrayToDataTable([
      ['Year', 'Expenses'],
      ['2004',      400],
      ['2005',      460],
      ['2006',       1120],
      ['2007',      540]
    ]);

    var options = {
      curveType: 'function',
      backgroundColor: { fill:'transparent' },
    };

    var chart = new google.visualization.LineChart(document.getElementById('curve_chart'));

    chart.draw(data, options);
  }

any solution ?