Color transition in WPF

I want to make a color transition of Background color of a WPF window.

How can I do this?

For example:

Brush i_color = Brushes.Red; //this is the initial color
Brush f_color = Brushes.Blue; //this is the final color

When I click on Button button1

private void button1_Click(object sender, RoutedEventArgs e)
{
    this.Background = f_color; //here the transition begins. I don't want to be quick. Maybe an interval of 4 seconds.
}