I just needed to make a fading effect with background colors, but it didn't work for me even if i did everything correct. I missed one important step that took me some precious time. I forgot to include the optional effects package, which contains the transitions between colors and classes.
Just included:

in the head of my page and the transitions between background colors started to work.
If you need to fade between background colors use this code:

$(document).ready(function(){



    $("selector_to_your_element").hover(

      function () {

        $(this).animate({

        backgroundColor: "red"

      }, 1000 );



      },

      function () {

		$(this).animate({

        backgroundColor: "blue"

      }, 1000 );      }

    );



  });

This will work when you hover over/out your mouse over an element.