Or, if they only care about the red color from the message highlight, after ignoring the "important" channels, the event could send that hack just 1 time for each message. It would blink each channel for just a split second

Code
on ^*:TEXT:*:#:{
  if (!$istok(#unimportantchannel1 #unimportantchannel2 ##maroon3,$chan,32)) return
  timer 1 0 window -g0 $chan
}