Thanks RXB and Ksarul for your responses.
I found the Amerisoft Expanded Graphics BASIC manual and gave its instructions a try. For some reason some of the commands don't seem to work, like CALL LINK("GRAFIC",0) produces a "BAD ARGUMENT" error message and CALL LINK("WINDOW",10,10) generates a 'SUBPROGRAM NOT FOUND' error message. However, CALL LINK("SETCOL,16,6) and CALL LINK("RECT",1,1,30,20) don't produce any error messages.
Running the program sent by senior_falcon I just realised that the 'WINDOW' command is not present in the APESOFT routines on mecha2.dsk, mind you 'GRAFIC' is. So, it seems that I may have a different version after all.