WPF Exception when try animating binding foreground

I have this control…:

<iconPack:PackIconAlvo
	Width="{StaticResource iconSize}"
	Height="{StaticResource iconSize}"
	HorizontalAlignment="Center"
	Foreground="{Binding IsMonitoringButtonActive, Converter={StaticResource IsSelectedToColorConverter}}"
	Kind="Monitoring"
	Style="{StaticResource AlarmAnimation}" />

…with this converter…:

public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
{
	return (bool)value ? new SolidColorBrush(Color.FromRgb(0, 255, 161)) : new SolidColorBrush(Color.FromRgb(131, 131, 131));
}

…and this animation style:

<Style x:Key="AlarmAnimation">
	<Style.Triggers>
		<DataTrigger Binding="{Binding IsAlarmForMonitoringButton}" Value="True">
			<DataTrigger.EnterActions>
				<BeginStoryboard>
					<Storyboard>
						<ColorAnimation
							AutoReverse="True"
							RepeatBehavior="Forever"
							Storyboard.TargetProperty="Foreground.(SolidColorBrush.Color)"
							From="Gray"
							To="Red"
							Duration="0:0:0.5" />
					</Storyboard>
				</BeginStoryboard>
			</DataTrigger.EnterActions>
		</DataTrigger>
	</Style.Triggers>
</Style>

When I start animation (IsAlarmForMonitoringButton == true) and IsMonitoringButtonActive == false, then I have error:

> Cannot animate 'Foreground.(0)' on an immutable object instance.

I can't deal with this error. It is important in this application that the foreground is variable, it is also important that it is animated when IsAlarmForMonitoringButton==true.

How can I handle this problem?

Set the Foreground property using a Style instead of using a binding expression and a converter, e.g.:

<iconPack:PackIconAlvo
        Width="{StaticResource iconSize}"
        Height="{StaticResource iconSize}"
        HorizontalAlignment="Center"
        Kind="Monitoring">
    <iconPack:PackIconAlvo.Style>
        <Style TargetType="iconPack:PackIconAlvo">
            <Setter Property="Foreground" Value="Yellow" />
            <Style.Triggers>
                <DataTrigger Binding="{Binding IsMonitoringButtonActive}" Value="True">
                    <Setter Property="Foreground" Value="Red" />
                </DataTrigger>
                <DataTrigger Binding="{Binding IsAlarmForMonitoringButton}" Value="True">
                    <DataTrigger.EnterActions>
                        <BeginStoryboard>
                            <Storyboard>
                                <ColorAnimation
                                    AutoReverse="True"                                
                                    RepeatBehavior="Forever"
                                    Storyboard.TargetProperty="Foreground.(SolidColorBrush.Color)"
                                    From="Gray"
                                    To="Red"
                                    Duration="0:0:0.5" />
                            </Storyboard>
                        </BeginStoryboard>
                    </DataTrigger.EnterActions>
                </DataTrigger>
            </Style.Triggers>
        </Style>
    </iconPack:PackIconAlvo.Style>
</iconPack:PackIconAlvo>

The other option is to apply the animation programmatically.