WPF Line 的颜色过度动画

            <Line Grid.Column="2" Grid.ColumnSpan="2" VerticalAlignment="Center" Height="20" Width="auto" StrokeThickness="5"                         
                          X1="0" Y1="10" X2="{Binding RelativeSource={RelativeSource Mode=Self},Path=ActualWidth}" Y2="10" x:Name="Line1">
                <Line.Stroke>
                    <LinearGradientBrush StartPoint="0,0"  EndPoint="1,0" >
                        <GradientStop Color="#FF94E894" Offset="0"/>
                        <GradientStop Color="#FF94E894" Offset="0.8"/>
                        <GradientStop Color="Black" Offset="0.8"/>
                        <GradientStop Color="Black" Offset="1"/>
                    </LinearGradientBrush>
                </Line.Stroke>
                <Line.Triggers>
                    <EventTrigger RoutedEvent="Loaded">
                        <BeginStoryboard>
                            <Storyboard>
                                <DoubleAnimation 
                    Storyboard.TargetProperty="(Line.Stroke).(LinearGradientBrush.GradientStops)[1].(GradientStop.Offset)"
                    BeginTime="00:00:00" Duration="00:00:5" From="0" To="1" AutoReverse="True" RepeatBehavior="Forever"/>
                                <DoubleAnimation
                    Storyboard.TargetProperty="(Line.Stroke).(LinearGradientBrush.GradientStops)[2].(GradientStop.Offset)"
                    BeginTime="00:00:00" Duration="00:00:5" From="0" To="1" AutoReverse="True" RepeatBehavior="Forever"/>
                            </Storyboard>
                        </BeginStoryboard>
                    </EventTrigger>
                </Line.Triggers>
            </Line>