1.2.2.6238-pre1 TabbedPage Actionbar background color

when I change the tabs in TabbedPage , the background color of Actionbar back to default color。

the code is :

    var mainTab = new TabbedPage() { Children = { ViewFactory.CreatePage<FirstPageViewModel>(), new SecondPage(),            ViewFactory.CreatePage<ThirdPageViewModel>() }, Title = "MobileOffice" };
   var mainPage = new NavigationPage(mainTab) { };
        mainPage.BarBackgroundColor = Color.Blue;
        mainPage.BarTextColor = Color.White;
        return mainPage;