Check Windows Phone 8.1 Theme and set a source property of an Image control

Check Windows Phone Theme

/// <summary>
/// This function checks if the light theme is active
/// and select black icons if it's the case
/// </summary>
private void CheckIconTheme()
{
  // Get the current Phone Background Theme (dark or light)
  SolidColorBrush brush = (SolidColorBrush)Resources["PhoneBackgroundBrush"];

  // If the light theme is active,
  // replace white icons with black ones
  if (brush.Color.Equals(Colors.White)) {
    
    // Create a new BitmapImage which will be 
    // the source of the Image Control defined in the xaml part
    BitmapImage bmi = new BitmapImage();
    bmi.CreateOptions = BitmapCreateOptions.IgnoreImageCache;
    
    // Set the URI that represents the path where the icon is located
    // Note that the path is prefixed with the required 'ms-appx:'.
    // The icons is in the phone's local storage
    bmi.UriSource = new Uri(" ms-appx:/Assets/Icons/iconCancel-black.png", UriKind.RelativeOrAbsolute);
    
    // These next 4 lines define the Source for the Image control
    CloseUsername.Source = bmi;
    CloseLanguage.Source = bmi;
    CloseDynamictile.Source = bmi;
    CloseBackground.Source = bmi;
  }
  else {
    // This means that the black theme is selected.
    // By default my icons are black
  }
}

// The code of the Image in the xaml part looks like this
// <Image x:Name="CloseUsername" 
//        Height="25" Width="25" 
//        Source="/Assets/Icons/iconCancel-white.png" 
//        Margin="10,0,0,0"
//        RenderTransformOrigin="0.5,0.5"/>