A formal specification of the look manager of a dialog system is presented. The look manager deals with the presentation of visual aspects of objects and the editing of those visual aspects. A formal model for specifying the look of objects based on the notion of texturing objects is presented. The texturing model is built from the observed real-life use of overlays of slides. The specification takes as a given hypothesis an invariant relation between the logical display of objects and their layout on the physical screen. The look on the screen is characterized as an invariant ideal show relation. The formalization achieves modularity for the look manager. The specifications are written using the Z notation. The experiment is an integral part of a larger effort in the formal design of a dialog system. It shows that the state-based specification methodology Z is very well suited for description of graphical interface software. Further, the formal specification yields insight into the inherent complexity of building graphical interfaces and their associated displays.>