Simultaneously pushing 9 and 1, or 7 and 3, on the Intellivision keypad should make a game pause. In original games by Mattel/APh, the screen was completely blanked using an EXEC routine. Later developers adopted the same design idea for accessibility but do not necessarily blank the screen.
Source Links:
media0101.intvprime.com/ba4ef/intellivision-echo/References-Unsorted/papaintellivision.com/pdfs-searchable/CCF10232011_00005.pdf