WPF Mouse Over Trigger

I have a ( i think) simple question

how to make a trigger on a rectangle, that switches color on mouse over?

i really dont get it :frowning: already tried so many xaml triggers

my rectangle is red, and what i need is, when you get with your mouse over my red triangle, the color changes into green (doesnt matter which colors).

need xaml code pls :slight_smile: -> using blend 3 (wpf) !!