Current window managers are based on the use of overlapping windows, which implies the notion of a window's depth. In order to facilitate the management of windows in desktop environments, recent work has explored their grouping into layers of non-overlapping windows. In this note, we investigate the effect of three visual depth cues on the perception of the depth of such layers: luminosity, blurring and shadow. The paper reports on a controlled experiment that indicates that luminosity helps users to assess the number of layers while blurring and shadow have no effect.