shading above/below intersection areas in line chart

[BigL76]

I have a net cash flow line chart which intersects with the x-axis in several instances, effectively creating areas of positive and negative cash flow.

How can I shade the areas above and below in a different colour each (e.g. green above, red below)?

Thanks!

[Andy Pope]

See here
http://www.andypope.info/ngs/ng33.htm

[BigL76]

Thanks Andy