System.Windows.Forms.DataVisualization.Charting.Chart chart1 = new System.Windows.Forms.DataVisualization.Charting.Chart();
this.Controls.Add(chart1);
chart1.ChartAreas.Add("area");

int[] x = { 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20 };
int[] y = { 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 9, 8, 7, 6, 5, 4, 3, 2, 1, 0 };

for (int i = 1; i <= 20; i++)
{
    chart1.Series.Add("series" + i.ToString());
    chart1.Series["series" + i.ToString()].Color = Color.FromArgb(255 - y[i] * 20, 0, 255 - y[i] * 10);
    chart1.Series["series" + i.ToString()].ChartType = System.Windows.Forms.DataVisualization.Charting.SeriesChartType.Line;
    chart1.Series["series" + i.ToString()].Points.AddXY(x[i-1], y[i-1]);
    chart1.Series["series" + i.ToString()].Points.AddXY(x[i], y[i]);
}

if (y[i] >= 7)
    chart1.Series["series" + i.ToString()].Color = Color.Red;
else
    chart1.Series["series" + i.ToString()].Color = Color.Blue;