GoldFish on your menu I wouldn't go with menu * as it can get messy if you have picwins an such just put in where you want to turn it off an on. imho i would use groups for the on an off

Example using groups with keeping your code the same:

menu menubar,channel,query {
  Turn Rainbow $iif($group(#rainbow) = on,Off,On):$+(.,$iif($group(#rainbow) = on,dis,en),able) #rainbow
}
#rainbow off
on *:input:*: {
  if ($left($1-,1) != /) {
    haltdef
    set -l %count 1
    while (%count <= $len($1-)) {
      set -l %rainbow %rainbow $+  $+ $gettok(04.07.08.09.11.13,$r(1,6),46) $+ ,01 $+ $iif($mid($1-,%count,1) != $chr(32),$mid($1-,%count,1),$chr(32) $+ $chr(32))
      inc %count
    }
    msg $active %rainbow
  }
}
#rainbow end

but whatever to each their own...