You can select predifined palette on the series:
Chart.Series[0].Palette = ChartColorPalette.Berry;
You can also define custom palette if you want using Chart.PaletteCustomColors... but the simpliest apptoach is to set individual data point Color property:
Chart.Series[0].Points[0].Color = Color.Red;
Chart.Series[0].Points[1].Color = Color.Green;
...
Alex.
http://blogs.msdn.com/alexgor