adding Foreground converter to DatagridTextColumn in xaml

I'm trying to add a converter to a DataGridTextColumn to convert the foreground brush based on the value of the cell in the xaml file. The DecimalConverter works fine and follows the same pattern.

Here is my xaml...

<UserControl.Resources>
    <y:FixedDecimalConverter x:Key="FixedDecimalConverter" />
    <y:ForegroundValueConverter x:Key="ForegroundV开发者_高级运维alueConverter" />       
</UserControl.Resources>
...
<data:DataGridTextColumn 
    Header="Absolute Return" 
    Binding="{Binding totalAbsoluteReturn.value, Converter={StaticResource FixedDecimalConverter}}"  
    Foreground="{Binding totalAbsoluteReturn.value, Converter={StaticResource ForegroundValueConverter}}" />

Here is the converter...

type ForegroundValueConverter() =
    interface  IValueConverter with
        member this.Convert(value, targetType, parameter, culture) = 
             let o: obj = upcast new SolidColorBrush(Colors.Red);
             o

        member this.ConvertBack(value, targetType, parameter, culture) = raise <| NotImplementedException()

...

Here is the error message

Message: Unhandled Error in Silverlight Application Code: 4004

Category: ManagedRuntimeError

Message: System.Windows.Markup.XamlParseException: AG_E_PARSER_BAD_PROPERTY_VALUE [Line: 29 Position: 32] at System.Windows.Application.LoadComponent(Object component, Uri resourceLocator) at Module1.MyIdeas..ctor() at Module1.Template..ctor() at Module1.MyApp..ctor()

Haven't tried it, but the folks oer there claim it works

http://forums.silverlight.net/forums/p/151524/338879.aspx#338879