The approach I like to use for similar tasks is to generate a PPM image file and then pipe the output to ppmtogif, like this:

  $RED = 255;
  $GREEN = 0;
  $BLUE = 0;

  open STDOUT, "| ppmtogif" or die "open: $!";
  # "1 1" means that the image is 1x1 pixel.
  # "255" means that 255 is the maximum color intensity.
  print "P3 1 1 255 $RED $GREEN $BLUE\n";
  close STDOUT or die "close: $!";
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This may not be as cool, and it has the disadvantage of requiring ppmtogif, but it's also a lot simpler, and it has the tremendous advantage that it's easy to generate images that are bigger than one pixel. For example, the images for this article were generated with this technique, as were these.

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