¿Hay alguna forma de animar unTextBox.ForegroundProperty?

<Color x:Key="NormalColor">#FF666666</Color>
<SolidColorBrush x:Key="NormalBrush" Color="{StaticResource NormalColor}" />

<Color x:Key="MouseOverColor">#FF666666</Color>
<SolidColorBrush x:Key="MouseOverBrush" Color="{StaticResource MouseOverColor}" />

<ControlTemplate x:Key="RegularTextBoxTemplate" TargetType="{x:Type TextBox}">
    <Grid>
        <VisualStateManager.VisualStateGroups>
            <VisualStateGroup x:Name="CommonStates">
                <VisualStateGroup.Transitions>
                    <VisualTransition GeneratedDuration="0:0:0.1"/>
                </VisualStateGroup.Transitions>
                <VisualState x:Name="Normal"/>
                <VisualState x:Name="MouseOver">
                    <Storyboard>
                        <!-- storyboard to animating foreground here... -->
                    </Storyboard>
                </VisualState>
            </VisualStateGroup >
        </VisualStateManager>
        <ScrollViewer x:Name="PART_ContentHost" 
                      BorderThickness="0"
                      IsTabStop="False"
                      Background="{x:Null}"/>
    </Grid>
</ControlTemplate>

<Style x:Key="RegularTextBox" TargetType="{x:Type TextBox}">
    <Setter Property="Foreground" Value="{StaticResource NormalBrush}"/>
    <Setter Property="Template" Value="{StaticResource RegularTextBoxTemplate}"/>
</Style>

Mis storyboards probados son:

<ColorAnimationUsingKeyFrames Storyboard.TargetName="PART_ContentHost"
                  Storyboard.TargetProperty="(Foreground).(SolidColorBrush.Color)">
    <EasingColorKeyFrame KeyTime="0" Value="{StaticResource MouseOverColor}" />
</ColorAnimationUsingKeyFrames>

<ColorAnimationUsingKeyFrames Storyboard.TargetName="PART_ContentHost"
              Storyboard.TargetProperty="(Control.Foreground).(SolidColorBrush.Color)">
    <EasingColorKeyFrame KeyTime="0" Value="{StaticResource MouseOverColor}" />
</ColorAnimationUsingKeyFrames>

<ColorAnimationUsingKeyFrames Storyboard.TargetName="PART_ContentHost"
          Storyboard.TargetProperty="(TextElement.Foreground).(SolidColorBrush.Color)">
    <EasingColorKeyFrame KeyTime="0" Value="{StaticResource MouseOverColor}" />
</ColorAnimationUsingKeyFrames>

<ColorAnimationUsingKeyFrames
                  Storyboard.TargetProperty="(Foreground).(SolidColorBrush.Color)">
    <EasingColorKeyFrame KeyTime="0" Value="{StaticResource MouseOverColor}" />
</ColorAnimationUsingKeyFrames>

<ColorAnimationUsingKeyFrames
              Storyboard.TargetProperty="(TextBox.Foreground).(SolidColorBrush.Color)">
    <EasingColorKeyFrame KeyTime="0" Value="{StaticResource MouseOverColor}" />
</ColorAnimationUsingKeyFrames>

<ColorAnimationUsingKeyFrames
              Storyboard.TargetProperty="(Control.Foreground).(SolidColorBrush.Color)">
    <EasingColorKeyFrame KeyTime="0" Value="{StaticResource MouseOverColor}" />
</ColorAnimationUsingKeyFrames>

<ColorAnimationUsingKeyFrames
          Storyboard.TargetProperty="(TextElement.Foreground).(SolidColorBrush.Color)">
    <EasingColorKeyFrame KeyTime="0" Value="{StaticResource MouseOverColor}" />
</ColorAnimationUsingKeyFrames>

Ninguno de ellos funciona. ¿Alguna idea? ¿Es incluso posible?