Perspective projection can be in an uncropped modeling view or in a cropped presentation view. The cropped perspective projection is set for the entire document on the Display tab of the Document Preferences dialog box; see Document preferences: Display tab.
In a cropped view, a clipping frame appears around the perspective view window, which is useful for presenting model elevations, for example. Drag the corners to increase or decrease the size of the window.
In an uncropped view, a shaded horizon representation is displayed in the background. The horizon provides a visual indication of the vertical position of the observer with respect to objects in the scene. The horizon does not print or export. The green color represents the ground below the horizon, and the blue color represents the sky above it, helping with orientation. The color of the ground and sky can be changed in the Interactive Appearance Settings dialog box; see Configuring interactive display.