ControlTemplate Storyboard color animation problem

I have a problem with color animation. This is my source:

 <Window.Resources>
    <hedit:BrushToColorConverter x:Key="BrushToColorConverter" />
    <Style x:Key="MyButtonStyle" TargetType="Button">
        <Setter Property="OverridesDefaultStyle" Value="True"/>
        <Setter Property="Margin" Value="5"/>
        <Setter Property="Template">
            <Setter.Value>
                <ControlTemplate TargetType="Button">
                    <ControlTemplate.Resources>
                        <Storyboard x:Key="buttonAnimIn">
                            <!-- Problem line -->
                            <ColorAnimation Storyboard.TargetName="bntBack" Storyboard.TargetProperty="Color" To="{Binding Path=Foreground, RelativeSource={RelativeSource AncestorType={x:Type UserControl}}, Converter={StaticResource BrushToColorConverter}}" />
                        </Storyboard>
                        <Storyboard x:Key="buttonAnimOut">
                            <ColorAnimation Storyboard.TargetName="bntBack" Storyboard.TargetProperty="Color" To="Blue" />
                        </Storyboard>
                        <Storyboard x:Key="buttonAnimForegroundIn">
                            <ColorAnimation Storyboard.TargetName="btnFore" Storyboard.TargetProperty="Color" To="Blue" />
                        </Storyboard>
                        <Storyboard x:Key="buttonAnimForegroundOut">
                            <ColorAnimation Storyboard.TargetName="btnFore" Storyboard.TargetProperty="Color" To="Red" />
                        </Storyboard>
                    </ControlTemplate.Resources>
                    <Border Name="border" 
                        BorderThickness="1"
                        Padding="4,2" 
                        BorderBrush="DarkGray" 
                        CornerRadius="3">
                        <Border.Background>
                            <SolidColorBrush Color="Blue" x:Name="bntBack" />
                        </Border.Background>
                        <ContentControl HorizontalAlignment="Center" VerticalAlignment="Center" Content="{TemplateBinding Content}">
                            <ContentControl.Foreground>
                                <SolidColorBrush Color="Red" x:Name="btnFore" />
                            </ContentControl.Foreground>
                        </ContentControl >
                    </Border>
                    <ControlTemplate.Triggers>
                        <EventTrigger RoutedEvent="Button.MouseEnter">
                            <BeginStoryboard Storyboard="{StaticResource buttonAnimIn}" />
                            <BeginStoryboard Storyboard="{StaticResource buttonAnimForegroundIn}" />
                        </EventTrigger>
                        <EventTrigger RoutedEvent="Button.MouseLeave">
                            <BeginStoryboard Storyboard="{StaticResource buttonAnimOut}" />
                            <BeginStoryboard Storyboard="{StaticResource buttonAnimForegroundOut}" />
                        </EventTrigger>
                    </ControlTemplate.Triggers>
                </ControlTemplate>
            </Setter.Value>
        </Setter>
    </Style>
</Window.Resources>

The problem is:

Cannot convert the value in attribute 'Style' to object of type 'System.Windows.Style'. Cannot freeze this Storyboard timeline tree for use across threads. Error at object 'System.Windows.Controls.Button' in markup file 'HLSLEditor;component/mainwindow.xaml' Line 223 Position 25.

When using fixed colors it worked, but it cannot work with the Foreground color of the parent...

How do I do an animation to the foreground or background color?

Thanks!