/// <summary>
    ///   <para>The color scheme used by the button.</para>
    /// </summary>
    /// <param name="widget">Widget to call method on.</param>
    /// <param name="colorScheme">Color scheme of button.</param>
    /// <returns>Reference to the current widget.</returns>
    /// <exception cref="ArgumentNullException">If <paramref name="widget"/> is a <c>null</c> reference.</exception>
    /// <seealso cref="IFacebookFollowButtonWidget.ColorScheme(string)"/>
    public static IFacebookFollowButtonWidget ColorScheme(this IFacebookFollowButtonWidget widget, FacebookColorScheme colorScheme)
    {
      Assertion.NotNull(widget);

      return widget.ColorScheme(colorScheme.ToString().ToLowerInvariant());
    }
    /// <summary>
    ///   <para>The color scheme used by the widget.</para>
    /// </summary>
    /// <param name="widget">Widget to call method on.</param>
    /// <param name="colorScheme">Color scheme of widget.</param>
    /// <returns>Reference to the current widget.</returns>
    /// <exception cref="ArgumentNullException">If <paramref name="widget"/> is a <c>null</c> reference.</exception>
    /// <seealso cref="IFacebookRecommendationsFeedWidget.ColorScheme(string)"/>
    public static IFacebookRecommendationsFeedWidget ColorScheme(this IFacebookRecommendationsFeedWidget widget, FacebookColorScheme colorScheme)
    {
      Assertion.NotNull(widget);

      return widget.ColorScheme(colorScheme.ToString().ToLowerInvariant());
    }
    /// <summary>
    ///   <para>Specifies visual color scheme of button.</para>
    /// </summary>
    /// <param name="widget">Widget to call method on.</param>
    /// <param name="scheme">Color scheme for button.</param>
    /// <returns>Reference to provided <paramref name="widget"/>.</returns>
    /// <exception cref="ArgumentNullException">If <paramref name="widget"/> is a <c>null</c> reference.</exception>
    /// <seealso cref="ITumblrShareButtonWidget.ColorScheme(string)"/>
    public static ITumblrShareButtonWidget ColorScheme(this ITumblrShareButtonWidget widget, TumblrShareButtonColorScheme scheme)
    {
      Assertion.NotNull(widget);

      return widget.ColorScheme(scheme.ToString().ToLowerInvariant());
    }