The following is a snippet that will allow you to programatically change the background and foreground color of the title bar in a Windows Store app from a code behind. In this case, I will be setting the bar to a dark gray color similiar to what is found in Visual Studio's dark color scheme. I typically put this code in the Loaded event of my main page but it also works fine from the loaded event in App.xaml.cs.
var titleBar = ApplicationView.GetForCurrentView().TitleBar;
if (titleBar != null)
titleBar.ButtonBackgroundColor = Color.FromArgb(255, 30, 30, 30);
titleBar.ButtonForegroundColor = Colors.White;
titleBar.BackgroundColor = Color.FromArgb(255, 30, 30, 30);
titleBar.ForegroundColor = Colors.White;