Binding GradientStop works but reports error - wpf

Question

The following code binds a GradientStop to the Background.Color property of TemplatedParent. Everything works but I am getting a binding error in the output window:
System.Windows.Data Error: 2 : Cannot find governing FrameworkElement or FrameworkContentElement for target element. BindingExpression:Path=Background.Color; DataItem=null; target element is 'GradientStop' (HashCode=6944299); target property is 'Color' (type 'Color')
<Window
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
x:Class="WpfBindingTest.MainWindow"
x:Name="Window"
Title="MainWindow"
Width="100" Height="100">
<Window.Resources>
<ControlTemplate x:Key="GradientTemplate" TargetType="{x:Type ContentControl}">
<Border BorderThickness="1" BorderBrush="{TemplateBinding Background}">
<Border.Background>
<LinearGradientBrush EndPoint="0.5,1" StartPoint="0.5,0">
<GradientStop Color="{Binding Path=Background.Color,
RelativeSource={RelativeSource TemplatedParent}}" Offset="1"/>
<GradientStop Color="White" Offset="0"/>
</LinearGradientBrush>
</Border.Background>
<ContentPresenter/>
</Border>
</ControlTemplate>
</Window.Resources>
<Grid x:Name="LayoutRoot">
<ContentControl Background="Green" Template="{StaticResource GradientTemplate}" >
<TextBlock VerticalAlignment="Center" HorizontalAlignment="Center" Text="X" />
</ContentControl>
</Grid>
</Window>

Answer 1

I also had the same error in the Visual Studio console output.
A possible explanation and workaround for this is reported here
Basically if you use a Converter that returns a LinearGradientBrush then you don't get the error
The code is something like this
[ValueConversion(typeof(System.Windows.Media.Color), typeof(LinearGradientBrush))]
class GradientConverter : IValueConverter
{
public object Convert(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
{
var brush = new LinearGradientBrush();
var color = (Color)value;
brush.StartPoint = new Point(0.5, 0);
brush.EndPoint = new Point(0.5, 1);
brush.GradientStops.Add(new GradientStop(Colors.White, 0));
brush.GradientStops.Add(new GradientStop((Color)value, 1));
return brush;
}
public object ConvertBack(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
{
throw new NotImplementedException();
}
}
And in the XAML
<Border BorderThickness="1" BorderBrush="{TemplateBinding Background}" Background="{Binding Path=Background.Color, RelativeSource={RelativeSource TemplatedParent}, Converter={StaticResource gradConv}}">