change the line color of google line chart

namespace OrthopedicSystem
{
    public partial class WebForm5 : System.Web.UI.Page
    {
        StringBuilder str = new StringBuilder();
        SqlConnection conn = new SqlConnection("Data Source=lakshi;Initial Catalog=orthopedics;Integrated Security=True");
        protected void Page_Load(object sender, EventArgs e)
        {
            if(!IsPostBack)
            {
                chart_bind();
            }
        }
        private DataTable GetData()
        {
            DataTable dt = new DataTable();
            conn.Open();
            string cmd = "Select * from score";
            SqlDataAdapter adp = new SqlDataAdapter(cmd, conn);
            adp.Fill(dt);
            conn.Close();
            return dt;
        }
        private void chart_bind()
        {
            DataTable dt = new DataTable();
            try
            {
                dt = GetData();

                str.Append(@"<script type=*text/javascript*> google.load( *visualization*, *1*, {packages:[*corechart*]}); 
google.setOnLoadCallback(drawChart);
            function drawChart() {
            var data = new google.visualization.DataTable();
            data.addColumn('string', 'Year');
            data.addColumn('number', 'score');
         
 
            data.addRows(" + dt.Rows.Count + ");");
 
            for (int i = 0; i <= dt.Rows.Count - 1; i++)
            {
                str.Append("data.setValue( " + i + "," + 0 + "," + "'" + dt.Rows[i]["visit_date"].ToString() + "');");
                str.Append("data.setValue(" + i + "," + 1 + "," + dt.Rows[i]["score"].ToString() + ") ;");
            }
           
            str.Append("   var chart = new google.visualization.LineChart(document.getElementById('chart_div'));");           
            str.Append(" chart.draw(data, {width: 660, height: 300, title: 'Company Performance',");           
            str.Append("hAxis: {title: 'Year', titleTextStyle: {color: 'green'}}");
            str.Append("}); }");
            str.Append("</script>");
            lt.Text = str.ToString().Replace('*', '"');   

            }
            catch { }
        }
    }
}