The text "The program is intentionally monochrome" doesn't match the image, which is mostly violet and green. That's because it doesn't use HPLOT correctly - on Apple IIe HPLOT green and orange only displayed in even columns, violet and blue in odd columns, and white only appears when adjacent odd and even columns are set. So line 6 should be: HPLOT2*INT(X(I)/2),Y(I):HPLOT2*INT(X(I)/2)+1,Y(I). (tested, actually plots white stars). Also at the original 1MHz, 20 stars is too slow to see that the stars form trails, it looks like random dot placement. It needs to be more like 5 stars.