This can be used to change the border colour.
where n is a number between 0 and 7.
As the ZX Spectrum manual states:
0 - black 1 - blue 2 - red 3 - purple, technically called magenta 4 - green 5 - pale blue, technically called cyan 6 - yellow 7 - white
- This function is 100% Sinclair BASIC compatible.