Try this:
Code:
alias testing {
  echo -a $+($chr(3),9,$chr(44),1) $+ $regsubex($1-,/(.*?)(\100).+?\50(.*?)\51/,$&
    $+($chr(3),3,\1,$chr(3),4,\2,$chr(3),3,$+($chr(40),$+($chr(3),4,\3,$chr(3),3),$chr(41))))
}
I know there may be better approaches with this, but this should work as intended.
Code:
/testing greentext@red(redtext)greentext