Line chart with changing colours depending on values

I only know of one way to do this (although other people may have other ideas). You have one set of data that is the returns. From that set you create two other parallel sets, one for the positive values, one for the negative. Then you create two lines, one black for positive and one red for negative. When you plot the data it will look like a single line that turns red when it goes negative.

If you post a workbook with some sample data I can provide a more detailed answer.

Positive negative chart.png