Override default colors in a Windows Phone RT app.

App.xaml.cs

#region custom methods
private void SetupCustomColors()
{
    SetColor("ProgressBarIndeterminateForegroundThemeBrush", ((SolidColorBrush)Current.Resources["VikingRed"]).Color);
    //SetColor("PivotHeaderForegroundUnselectedBrush", ((SolidColorBrush)Current.Resources["VikingGrey"]).Color);
    SetColor("PivotHeaderForegroundSelectedBrush", Colors.White);
}

private void SetColor(string resource, Color color)
{
    if (!Resources.ContainsKey(resource))
        return;
    var brush = Resources[resource] as SolidColorBrush;
    if (brush != null)
        brush.Color = color;
}
#endregion

Hi, could you teach me how to use this code to override the theme color?
I copy your code to my app.xaml, but it did not work on my windows phone runtime.
Thanks for every help.