使用触发器更改XAML地图图钉的背景颜色

I'm trying to change the background color of the XAML map pushpins using a DataTemplate trigger, but maybe there is something wrong in my code. The idea is that the ItemSource of the map is binded to an ObservableCollection of PushpinModel and when the value of the property IsOnline is true, then the pushpin should became green.I'm trying to change the background color of th