JFreeChart BarChart -> NO gradient

The source code for an older version of org.jfree.chart.demo.BarChartDemo1 shows how to set the series colors. Just specify plain colors instead of gradients.

renderer.setSeriesPaint(0, Color.red);
renderer.setSeriesPaint(1, Color.green);
renderer.setSeriesPaint(2, Color.blue);

Correction: The key to @Jes's helpful answer may be found in the initialization of defaultBarPainter in BarRenderer.

Before you create the chart from ChartFactory you can set the chart theme:

ChartFactory.setChartTheme(StandardChartTheme.createLegacyTheme());

The default is the JFreeTheme which adds the gradient. The following themes are available:

ChartFactory.setChartTheme(StandardChartTheme.createJFreeTheme());
ChartFactory.setChartTheme(StandardChartTheme.createDarknessTheme());

The problem lies in the BarPainter you are using. The JFreeChart version 1.0.13 default is to use GradientBarPainter which adds a metallic-ish look to the bar. If you want the "old" look the solution is to use the StandardBarPainter.

final CategoryPlot plot = chart.getCategoryPlot();
((BarRenderer) plot.getRenderer()).setBarPainter(new StandardBarPainter());

That should do it.

Alternatively, if you want use JFreeChart's BarRenderer, you could force it to use the StandardBarPainter by calling the static method setDefaultBarPainter() before initializing your renderer.

final CategoryPlot plot = chart.getCategoryPlot();
BarRenderer.setDefaultBarPainter(new StandardBarPainter());
((BarRenderer) plot.getRenderer()).setBarPainter(new BarPainter());

If you want more control of the chart you can always build it from the ground up instead of using ChartFactory, but that does require a lot extra code.