How call OnPropertyChanged in double embedded data in xamarin? - xamarin.forms

Question

I have a Content page, which contain CollectionView inside CarouselView.
First time when the page is loading the double embedded binding is work fine. Show everithing correctly.
But when i try to change embedded property value nothing happen. How update these properties?
formChooseElement.formViewerElements[0].formViewerElementAnswares[0].color=Color.Green;
Like:
<CarouselView ItemsSource="{Binding formViewerElements}">
<CarouselView.ItemTemplate>
<DataTemplate>
<StackLayout>
<Label Text="{Binding text}" />
<CollectionView ItemsSource="{Binding formViewerElements}" >
<CollectionView.ItemTemplate>
<DataTemplate >
<StackLayout BackgroundColor="{Binding color}">
<Label Text="{Binding text}" >
</StackLayout>
</DataTemplate>
</CollectionView.ItemTemplate>
</CollectionView>
</StackLayout>
BindingContext in code behind:
this.BindingContext = new FormViewerViewModell();
ViewModell:
public class FormViewerViewModell : INotifyPropertyChanged
{
public FormViewerViewModell()
{
GenerateData
}
private FormChooseElement FormChooseElement;
public FormChooseElement formChooseElement
{
get => FormChooseElement;
set
{
FormChooseElement = value;
OnPropertyChanged(nameof(FormChooseElement));
}
}
public ObservableCollection<FormViewerElement> formViewerElements
{
get => formChooseElement.formViewerElements;
set
{ formChooseElement.formViewerElements = value;
OnPropertyChanged(nameof(formChooseElement.formViewerElements));
}
}
public event PropertyChangedEventHandler PropertyChanged;
protected virtual void OnPropertyChanged([CallerMemberName] string propertyName = null)
{
PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
}
}
FormChooseElement
public class FormChooseElement
{
public ...
public ObservableCollection<FormViewerElement> formViewerElements { get; set; }
}
FormViewerElement
public class FormViewerElement
{
public ...
public ObservableCollection<FormViewerElementAnsware> formViewerElementAnswares { get; set; }
}
FormViewerElementAnsware
public class FormViewerElementAnsware
{
public ...
public Color color { get; set; };