The subroutine below enables you to select any of the colour registers (0-4) and alter the colour value held there. The machine code routine is loaded into page 6 of the RAM and set up to execute within the vertical blank interrupting procedure.
After enabling the routine by GOSUB 9400 you can alter the colours by pressing the console keys:
OPTION - selects the next colour register SELECT - increases the colour value START - decreases the colour value
Once the routine is installed you should be able to use the machine normally and run other programs (providing they don't use the three function keys, page 6 RAM or their own VBI routine). Thus you can experiment with the colours produced by program displays.
Nick Pearce, St. Leonards