This was my quest.
poke 53281,0 changes the background colour.
Then open monitor
this does nothing.
I watched this video
the comments are my own. Luckily I made a typo I wrote ldx not ldz because I'm just wired to press x and not z I guess. And all was well. It worked. However BASIC wouldn't return it just hung.
So I added another
to put everything back to 0 and all was good. The nop helps of cause as the first map is a hidden sei.
So how does this differ from running code in the monitor?
then I noticed my mistake with the LDX not LDZ and fixed it so it was as shown above, and as per the video.
It broke, it doesn't do anything anymore.
So I thought I understood it, but seems I don't.