Scenarios can overload individual entries of the global Graphics.ocg group as well as add new content like a sky background image or loader graphics (*.png or *.jpg). Sky graphics should either be tileable or big enough that it won't even tile if the player zooms out very far. Loader screen are displayed while the scenario is loading. If multiple files are present (Loader1.png, Loader2.png, Loader3.png...), one is selected randomly. You can optionally specify which loader to use in Scenario.txt. Loader image files located in parent scenario folders are also used.See
overloading rules.