Yankes, neighbor stripes should be "smoothed" but not overlapped through each other. Unfortunately this depends on zoom level. While this picture is quite acceptable, zoomed out picture will look more "noised" at twilight zone.
I suppose you've set rand()%8 value? I prefer %4, though %8 is much better than %20 which was at first. Flaw of this "smoothing" approach is indistinguishable "full night" and "full day" line.
I've attached vs2003 built version. Which is, I suppose, quite old (in terms of git branches).