SilverLight的一个问题

xaml文件预览如下: <Grid x:Name="LayoutRoot" Background="White">
        <Grid.RowDefinitions>
            <RowDefinition Height="120"></RowDefinition>
            <RowDefinition Height="120"></RowDefinition>
        </Grid.RowDefinitions>
        <Grid.ColumnDefinitions>
            <ColumnDefinition Width="200"></ColumnDefinition>
            <ColumnDefinition Width="*"></ColumnDefinition>
        </Grid.ColumnDefinitions>
        <Rectangle x:Name="PreviewColor" Grid.Row="0" Grid.Column="1" Fill="#FF6600" Margin="10" Stroke="Black" StrokeThickness="2"></Rectangle>
        <StackPanel Grid.Row="1" Grid.Column="1">
            <TextBlock FontSize="12">Color</TextBlock>
            <TextBox x:Name="HexColor" Width="160" Height="30" Margin="10,5" FontSize="11" Text="#FF6600"></TextBox>
        </StackPanel>
        <StackPanel Grid.Row="0" Grid.Column="0" Grid.RowSpan="2" VerticalAlignment="Center">
            <TextBlock FontSize="12" Text="Alpha" Margin="10,15,0,0"></TextBlock>
            <Slider x:Name="SliderAlpha" Margin="20,0,10,0" Maximum="255" Value="255" ValueChanged="SliderAlpha_ValueChanged" ></Slider>
            <TextBlock FontSize="12" Text="Red" Margin="10,15,0,0"></TextBlock>
            <Slider x:Name="SliderRed" Margin="20,0,10,0" Maximum="255" Value="255" ValueChanged="SliderAlpha_ValueChanged"></Slider>
            <TextBlock FontSize="11" Text="Green" Margin="10,15,0,0"></TextBlock>
            <Slider x:Name="SliderGreen" Margin="20,0,10,0" Maximum="255" Value="102" ValueChanged="SliderAlpha_ValueChanged"></Slider>
            <TextBlock FontSize="12" Text="Blue" Margin="10,15,0,0"></TextBlock>
            <Slider x:Name="SliderBlue" Margin="20,0,10,0" Maximum="255" Value="0" ValueChanged="SliderAlpha_ValueChanged"></Slider>
        </StackPanel>
    </Grid>编辑了ValueChanged="SliderAlpha_ValueChanged"事件处理代码后  运行页面一直处于100%的状态 不显示
ValueChanged="SliderAlpha_ValueChanged" 代码如下:
  private void SliderAlpha_ValueChanged(object sender, RoutedPropertyChangedEventArgs<double> e)
        {
            Color color = Color.FromArgb((byte)SliderAlpha.Value, (byte)SliderRed.Value, (byte)SliderGreen.Value, (byte)SliderBlue.Value);
            PreviewColor.Fill = new SolidColorBrush(color);
            HexColor.Text = color.ToString();
        }请问是怎么回事