Tint Problems in Actionscript

Hi,
I have recently been trying to create the necessary code in Actionscript to allow a movie clip to change Tint randomly and gradually. After looking at other similar posts I was able to work out how to make the Tint of an object change with code. However I have been using a switch statement (which isnt practical) and with the method I have used it is not possible to change the opacity value of the tint, so the object changes colour instantly rather than fading into it.

The method I am currently using is:

var colour = new Color(myMovieClip);
colour.setTransform({rb:100, aa:20});

Any help is appreciated.
Thanks.