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VERTICAL RAINBOW

By Virender Dayal

Unlike the usual horizontally scrolling rainbows that people are used to on the Atari, this program rotates vertical bands of shaded color on a GTIA Graphics 9 screen. Using the vertical blank interrupt (VBI), it changes the colors every 1/60 of a second. It also creates a window at the bottom of the screen, where you can enter color changes while the program runs.

http://www.atarimagazines.com/v8n8/techtips.html