JFreeChart _chart = ChartFactory.createTimeSeriesChart(......);

  XYPlot _xyplot=(XYPlot) _chart.getPlot();

  XYLineAndShapeRenderer xylinerenderer=(XYLineAndShapeRenderer)_xyplot.getRenderer();

    //以下分別給同一個曲線圖中3條曲線設定顏色,0為第一條1為第二條,2為第三條

    xylinerenderer.setSeriesPaint(0, new Color(0, 0 ,255 ));  或者 xylinerenderer.setSeriesPaint(0, Color.BLUE);
    xylinerenderer.setSeriesPaint(1, new Color(255 ,215, 0 ));
    xylinerenderer.setSeriesPaint(2, new Color(0, 238, 118));