property Bar.HistogramGridLinesColor as Color
Retrieves or sets a value that indicates the color to show the histogram's grid lines.

TypeDescription
Color A Color expression that specifies whether the grid lines are shown in the histogram. Use the value on 1, incase you actually need a black grid lines color.
By default, the HistogramGridLinesColor property is 0, which means that it has no effect. If the HistogramGridLinesColor property is not 0, it indicates the color to show the grid lines in the histogram. The grid lines for the histogram are shown only if the HistogramType property is exOverload and they are shown only in the right part of the histogram. Instead, you can use the HistogramRulerLinesColor property to specify the color to show the bar's histogram ruler that are always shown in the left part of the histogram. You can always use the BeforeDrawPart/AfterDrawPart events to provide your custom drawing in the histogram.

The following screen show shows the grid lines color in the right side of the histogram: