You can change the colors of the background and grid you see in the Viewer window. The scene you see in the Viewer window is always seen through a camera view (see Camera view). Therefore, the background color depends on which camera you are currently using to view the scene (referred to as the current camera).
You can show or hide the scene’s grid using the Camera settings as well (see Showing the Viewer window grid), but change the grid’s color from the Preferences window.
See also Camera settings.
To change the background color:
Navigator window A. Current camera selected in Scene browser B. Background Color settings in Camera Settings pane
Preferences window A. Select Viewer B. Grid Color settings