That's because ST High does not really have color registers, its always black and white. Later models like the TT030 had what was called duo-chrome which would allow you pick the 2 colors. Basically, that trick won't work on a regular ST.
You could try speeding up the copy to the screen. I'm not sure why the example moves it in 80 byte chunks when the screen ram is a linear block of ram. One line of code should suffice. The loop can be removed.
Try this instead:
Code: Select all
adr%=XBIOS(2) ! Start of screen memory
BMOVE x%+34,adr%,32000 ! Move data to screen (in one go)