<Window x:Class="WpfApplication2.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:local="clr-namespace:WpfApplication2"
        Title="MainWindow" Height="350" Width="525">
    <Window.Resources>
        <SolidColorBrush x:Key="MyBrush" Color="Yellow"></SolidColorBrush>
        <Style TargetType="Label" x:Key="MyLabel">
            <Setter Property="Template">
                <Setter.Value>
                    <ControlTemplate TargetType="Label">
                        <ControlTemplate.Triggers>
                            <EventTrigger RoutedEvent="Button.MouseEnter">
                                <EventTrigger.Actions>
                                    <BeginStoryboard>
                                        <Storyboard>
                                            <ColorAnimation Storyboard.TargetName="TB" Storyboard.TargetProperty="Background.Color"   To="{Binding Source={StaticResource MyBrush}, Path=Color}" 
                                            Duration="0:0:1"></ColorAnimation>
                                        </Storyboard>
                                    </BeginStoryboard>
                                </EventTrigger.Actions>
                            </EventTrigger>
                        </ControlTemplate.Triggers>
                        <Border Background="Blue" Name="TB">
                            <Label>123</Label>
                        </Border>
                    </ControlTemplate>
                </Setter.Value>
            </Setter>
        </Style>
    </Window.Resources>
    <Border>
        <Label Style="{StaticResource MyLabel}"></Label>
    </Border>
</Window>

<Storyboard>
    <ColorAnimation Storyboard.TargetName="TB" Storyboard.TargetProperty="Background.Color" To="{Binding Source={StaticResource MyBrush}, Path=Color}" Duration="0:0:1"></ColorAnimation>
</Storyboard>