Found this for change to change the color of the backbutton .
NavigationPage.SetIconColor(this, Color.FromHex("#FFFF00"));
The backgroudcolor of the page i change with DynamicResource.
App.Current.Resources["defaultBackgroundColor"] = Preferences.Get("BackgroundColor", "#1D252D");
For the Backcolor of the backbutton i tryed this but not working because i think ,can i change the FromHex part in to ?
NavigationPage.SetIconColor(this, Color.FromHex("{DynamicResource defaultBackgroundColor}"));
