borderColor

Sets the color of the border for the hovered bars:

seriesSettings: {
    bar: {
        enablePointSelection: true,
        activeSettings: {
            pointHoveredState: {                
                color: "red",
                borderColor: "green",
                borderWidth: 12,
                borderRadius: 5
            }
        }
    }
}

This setting is demonstrated in the following example.