This shows an example of 3 post-process passes, each of them adding a light Red, Green and Blue color to the previous pass, yielding a white-ish image.
Use Alt+Mouse to manipulate the camera using MAYA mode.
Use Alt+Shift+Mouse to manipulate the camera using UnrealEd mode (i.e. first person).
If you are under Linux and can't use the Alt key, push that button so everything works without Alt.