An exception is thrown when setting the ChartPallete FillColor property. The issue is reproduced on all platforms.
Workaround:
Also set the StrokeColor property.
<telerik:ChartPalette>
<telerik:ChartPalette.Entries>
<telerik:PaletteEntry FillColor="Red" StrokeColor ="Yellow"/>
<telerik:PaletteEntry FillColor="Gray" StrokeColor ="Yellow" />
<telerik:PaletteEntry FillColor="Blue" StrokeColor ="Yellow"/>
</telerik:ChartPalette.Entries>
</telerik:ChartPalette>