As Erel clears the canvas with a transparent color in his Canvas library, I replicated the same behavior in my AcSf lib but it's not a property of the transparent color (we use the PorterDuff mode CLEAR when the color parameter is 0). That being said, each time the Draw event is raised in your app, the view contains only the background (any previous drawing is cleared). So clear the background if you have one (by setting it to null) and you'll get a totally empty surface.