It's a bit long but this colors the nick the same as mirc does.
$+(<,,$nick($chan,$nick).color,$iif($left($nick($chan,$nick).pnick,1) isin $prefix,$v1),$nick,>)
Just replace the "$+(<, $left($nick(#, $nick, a, r).pnick, 1), $nick, >)" part with that and you should be good