Yes, it is possible. It's probably best to start with a clear background first, but you can change it as long as you haven't merged any layers with a colored background during your creating process. Whether you start with a clear background or change it later, you're going to want to set the "Opacity" dial to read "0%". Here are the steps to change to a layers canvas opacity (illustrated in the attached image):
Step 1: Click on the black arrow of the layer with a solid canvas background.If you plan to start with a new painting, just change the Opacity setting at the creation stage.
Step 2: Select "Edit Paper Settings" from the layer menu.
Step 3: Change the canvas settings Opacity dial to read "0%".
Step 4: Click "OK" to accept the changes.