Demo Main Tile (Switch Tile Color background) Win RT 8.1

btColored

// Just put diferent images (transparents and colored) and change like this...

private async void btColored_Tapped(object sender, TappedRoutedEventArgs e)
{
    var folder = Windows.ApplicationModel.Package.Current.InstalledLocation;
    var assetsfolder = await folder.GetFolderAsync("Assets");

    var file = await assetsfolder.GetFileAsync("squaretile-sdkWithColor.png");
    var oldfile = await assetsfolder.GetFileAsync("squaretile-sdk.png");

    await file.CopyAndReplaceAsync(oldfile);

    TileUpdateManager.CreateTileUpdaterForApplication().Clear();
}

btTransparent

private async void btTransparent_Tapped(object sender, TappedRoutedEventArgs e)
{
    var folder = Windows.ApplicationModel.Package.Current.InstalledLocation;
    var assetsfolder = await folder.GetFolderAsync("Assets");

    var file = await assetsfolder.GetFileAsync("squaretile-sdkWithOutColor.png");
    var oldfile = await assetsfolder.GetFileAsync("squaretile-sdk.png");

    await file.CopyAndReplaceAsync(oldfile);

    TileUpdateManager.CreateTileUpdaterForApplication().Clear();
}