NavigationPage BarTextColor is not working in android 5.0

I set the BarTextColor at NavigationPage. Its working on android 4.0.
But the color is not changing when install on android 5.o and above.

My code is as follow:
NavigationPage nav = new NavigationPage(new MainDelivery());
nav.BarBackgroundColor = Color.FromHex("#27252b");
nav.BarTextColor = Color.FromHex("#C0C0C0"); //Silver

Any ideas would be appreciated.