Series.InvertColorIndex (Word)

Returns or sets the fill color for negative data points in a series. Possible return values are xlColorIndexAutomatic - Automatic color, xlColorIndexNone - No color.

The InvertColorIndex property enables you to set the fill color for negative data points as a color index value from 0 to 56. Instead of using the InvertColorIndex property, you can use the InvertColor property, which enables you to set the color as a specific numeric, hexadecimal, octal, or RGB color value.

ActiveDocument.Background.Chart.FullSeriesCollection(1).InvertColorIndex = RGB(0,0,255)'blue