silverlight datagrid 的ColumnHeader 背景色没用,该怎么解决

silverlight datagrid 的ColumnHeader 背景色没用
以下是代码：

<data:DataGrid.ColumnHeaderStyle>
                        <Style TargetType ="prim:DataGridColumnHeader">
                            <Setter Property="FontSize" Value="12"></Setter>
                            <Setter Property="Background" Value="Red"></Setter>
                        </Style>
                    </data:DataGrid.ColumnHeaderStyle>

不变色啊，急！！！
------解决方案--------------------------------------------------------

<UserControl x:Class="SilverlightApplication1.MainPage"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
    xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
    mc:Ignorable="d"
    d:DesignHeight="300" d:DesignWidth="400" xmlns:sdk="http://schemas.microsoft.com/winfx/2006/xaml/presentation/sdk">
    <UserControl.Resources>
        <Style x:Key="DataGridColumnHeaderStyle1" TargetType="sdk:DataGridColumnHeader">
            <Setter Property="Template">
                <Setter.Value>
                    <ControlTemplate TargetType="sdk:DataGridColumnHeader">
                        <Grid x:Name="Root">
                            <Grid.ColumnDefinitions>
                                <ColumnDefinition/>
                                <ColumnDefinition Width="Auto"/>
                            </Grid.ColumnDefinitions>
                            <Rectangle x:Name="BackgroundRectangle" Grid.ColumnSpan="2" Fill="#FF1F3B53" Stretch="Fill"/>
                            <Rectangle x:Name="BackgroundGradient" Grid.ColumnSpan="2" Stretch="Fill" Fill="Red"/>