Inverse characters on a graphics screen using a special font

One-line subroutine you may use often is a way to get inverse characters on a graphics screen when using a special font. The font’s address is always determined this way: POKE 756,(hi-byte only, lobyte=0);

I use the following subroutine to invert the character set from the value it has at that time:

A=PEEK(756)*256:FOR I=0 TO 1023: POKE A+I,255-PEEK(A+I):NEXT I: RETURN