Try this code:
Code:
on ^*:TEXT:**:?,#:{
  var %s, %r = /\030? $+ $color(background) $+ (?!,\d{0,2}) $+ /g
  %r = $regsub(,$1-,%r,,%s)
  if (!$window($target)) query $target
  echo -tl $target < $+ $nick $+ > %s
  haltdef
}


It should remove any color codes that have a foreground color that is the same as your background color, unless there is a background color included with the color code.

Example:

(assuming you background color is white - 0)
([] = ctrl+k)
[]0TEXT = color code removed
[]00TEXT = color code removed

[]00,01TEXT = color code not removed
[]00,00TEXT = color code not removed
[]12TEXT = color code not removed
[]12,00TEXT = color code not removed
[]12,15TEXT = color code not removed

-genius_at_work