japhy, you might find Coloring IRC logs nicely interesting, too.

This is the algorithm my IRC bot iblechbot uses, too (screenshot).

First, a raw IRC log is read to find out which nicks were online (and talked) at the same time. This information is used to build a interference graph. Then, using the graph, all nicks get distict colors.

Because of the interference graph, the colors used are reduced to a minimum:

• 10:00 - A joins - color: 1/3 # notice: three colors needed
• 10:03 - B joins - color: 2/3
• 10:05 - C joins - color: 3/3
• (Time passes...)
• 20:00 - D joins - color: 1/2 # notice: only two colors used here
• 20:02 - E joins - color: 2/2

Using the colornum/total_num_of_colors information, the actual color pair (foreground, background) is built:

sub calc_color {
  my ($i, $ncolors) = @_;
    $ncolors = 1 if $ncolors == 0; # No division /0.

  my $a = 0.95;     # tune these for the starting and ending concentra
+tions of R,G,B
  my $b = 0.5;
  my $rgb = [ [$a,$b,$b], [$b,$a,$b], [$b,$b,$a], [$a,$a,$b], [$a,$b,$
+a], [$b,$a,$a] ];
  my $rgbmax = 125;   # tune these two for the outmost ranges of colou
+r depth
  my $rgbmin = 240;

  my $n = $i % @$rgb;
  my $m = $rgbmin + ($rgbmax - $rgbmin) * ($ncolors - $i) / $ncolors;

  my @c = map { $rgb->[$n][$_] * $m } 0 .. 2;
  my $g = $c[0] * .3 + $c[1] * .59 + $c[2] * .11;
  my $f = $g > 127 ? "#000000" : "#ffffff";
  my $h = sprintf "#%02x%02x%02x", @c;

  ($f, $h);
}
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