Simplest way is to grab the top edge of the superimposed event on the higher track and pulling it down – this will reduce its opacity from 99% to zero.
You can also Add a Compsite level envelope to a whole track, then drag it up and down like volume.
Then you can play with the opacity of the lower track, or placing colour, pattern or gradient beneath, etc., etc.
Peter Wright
Perth, Western Oz
http://www.allroundvision.com.au