on *:text:*:#channel:{
if ($me isop $chan) {
if ($chr(3) isin $1-) { ban -k $chan $nick 2 Colour is not allowed. }
}
}
Replace #channel with your channel name.
The "2" makes the script ban *!*@host If you want something different, take a look at $mask
/help ban
/help $mask
or
https://en.wikichip.org/wiki/mirc/commands/banhttps://en.wikichip.org/wiki/mirc/identifiers/$mask