public ChartFillBase Fill {get; set;}
This property returns null by default, indicating that no fill is applied. In this case, the default fill color for the associated Series is used.
To apply a solid color fill, assign an instance of the ChartSolidFill class to this property.
To apply a gradient fill, assign an instance of the ChartGradientFill class to this property.
Target Platforms: Android 4.4+, iOS 8+
Development Environments: Visual Studio 2015+, Visual Studio for Mac Preview, Xamarin for Visual Studio 4.2+