I'm changing the TextBlock color through the trigger, after 5 seconds, I would like to switch the color back to the TextBlock's initial, default color that is defined in the resource dictionary, without defining the color explicitly.
Here is the TextBlock style I use:
<Style BasedOn="{StaticResource {x:Type TextBlock}}" TargetType="{x:Type TextBlock}">
    <Style.Triggers>
        <DataTrigger Binding="{Binding IsSelected}" Value="True">
            <Setter Property="Foreground" Value="{StaticResource LightBackgroundBrush}" />
            <!--  Go back to initial color  -->
            <DataTrigger.EnterActions>
                <BeginStoryboard>
                    <Storyboard>
                        <ColorAnimation
                            BeginTime="0:0:05"
                            Storyboard.TargetProperty="Foreground.Color"
                            To="???" />
                    </Storyboard>
                </BeginStoryboard>
            </DataTrigger.EnterActions>
        </DataTrigger>
    </Style.Triggers>
</Style>
I mean this line specifically:
<ColorAnimation
   BeginTime="0:0:05"
   Storyboard.TargetProperty="Foreground.Color"
   To="???" />
I have tried setting To property to {x:Null} markup extension, however the color remains the same.
How can I make it animate to the default color?
edit
Since @Rekshino marked this question as a possible duplicate, I want to state that there is no relation between my question and the question linked by him, hence question might have been misunderstood by him as I haven't asked about To property bindings.