If I recall correctly you could run CGA and Hercules and the same time as they used different memory areas.
There were even a few debuggers that used this into the VGA era - program would be on the color monitor and your debugger on the black and white (actually usually orange or green).
There were even a few debuggers that used this into the VGA era - program would be on the color monitor and your debugger on the black and white (actually usually orange or green).