<ResourceDictionary xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">
    <Style x:Key="Rect" TargetType="Rectangle">
        <Style.Triggers>
            <Trigger Property="IsMouseOver" Value="True">
                <Setter Property="Fill" Value="Azure"></Setter>
            </Trigger>
        </Style.Triggers>
    </Style>
</ResourceDictionary>
...
...
...
<Rectangle Grid.Column="1" Style="{StaticResource Rect}" Width="30" Height="30"></Rectangle>