public ActionResult UpdateWidgetColor( [Bind(Include="Color,ID")]Widget widget )
{

}

public ActionResult UpdateWidgetColor( int id, string color )
{

   var whitelist = new string[] { "Color" };

   Widget widget = db.Widgets.SingleOrDefault( w => w.ID == id );

   if (widget == null) ...handle missing widget error

   if (!TryUpdateModel( widget, whitelist ))
   {
      ...
   }
   else
   {

   }
}