CategoryPlot categoryplot = (CategoryPlot) jfreechart.getPlot();
CategoryItemRenderer categoryitemrenderer = categoryplot.getRenderer();
BarRenderer barrenderer = (BarRenderer) categoryitemrenderer;
// 拿到之后,额可以用Index直接设置
barrenderer.setSeriesPaint(3, new Color(255, 0, 0));
// 也可以根据系列的数值,获得Index,然后在设置颜色
barrenderer.setSeriesPaint(categorydataset.getRowIndex("<200米"), new Color(255, 0, 0));