It depends on what specifically you are trying to do. If you are displaying a stacked bar, and want the different statuses of the stack to be different colors, use the "General color settings" in the Chart Editor on the Chart tab of the report definition:

This allows you to define the colors that the chart will use first when displaying the stacked columns. I believe it will use them in the order that they appear in the list you enter, so match that to the order that the statuses appears in the stacked columns (i.e., the order of the legend).

If you are trying to display different columns for specific "group by" values in different columns, use the "Conditional colors" settings in the Chart editor on the report definition:

I have an example that shows a count of cases less than a month old in green and a month or more in red:

The report groups by a function alias that returns either "Month Old" or "Less Than Month Old":

When is runs, the columns show in the specified colrs:

Hope this helps!