how to change navigation bar text color in xamarin forms android

my xamarin forms using cross platform application android version bartextcolor property does not work ! . barbackroundcolor property was changed.but bartextcolor does not chanaged i am using the code is

MainPage = new NavigationPage {BarBackgroundColor=Color.Lime, BarTextColor = Color.Purple}; The first property was worked ,second property not worked .pld kindly me answer