Xamarin.Forms Почему не в цикле не меняется цвет

Grid grid = new Grid
{
   RowDefinitions =
   {
       new RowDefinition { Height = new GridLength(1, GridUnitType.Star) },
       new RowDefinition { Height = new GridLength(1, GridUnitType.Star) },
       new RowDefinition { Height = new GridLength(1, GridUnitType.Star) }
   },
   ColumnDefinitions =
   {
       new ColumnDefinition { Width = new GridLength(1, GridUnitType.Star) },
       new ColumnDefinition { Width = new GridLength(1, GridUnitType.Star) },
       new ColumnDefinition { Width = new GridLength(1, GridUnitType.Star) }
   },
   Margin = new Thickness(30)
};
Label label = new Label
{
   Text = "eyhetgrd6rutb"
};
BoxView tealBox = new BoxView { Color = Color.Teal, Margin = 0, CornerRadius = 9 };
grid.Children.Add(tealBox, 1, 0);
Grid.SetRowSpan(tealBox, 3);
TapGestureRecognizer tapGesture = new TapGestureRecognizer
{
    NumberOfTapsRequired = 2
};
tapGesture.Tapped += (s, e) =>
{
     count++;
     label.Text = string.Format("Вы нажали {0} раз", count);
     tealBox.Color = Color.Red;
     Thread.Sleep(100);
     while(tealBox.Opacity>0)
     {
          Thread.Sleep(100);
          tealBox.Opacity = tealBox.Opacity - 0.1;
     }
     tealBox.Color = Color.black;
     tealBox.Opacity = 1;
};
label.GestureRecognizers.Add(tapGesture);

 label.Text = string.Format("Вы нажали {0} раз", count);