There was also the screen border which generally had to have one color but you could use a similar trick to draw static stripes on it (ZX wasn't fast enough to change the color more than a few times per scan line, so you could not really draw more than stripes of varying width).

I remember a game that had a welcome screen which had matching stripes on the real screen and then drew some pixel patterns on it to create an illusion of drawing individual pixels on the border.