I'd like to propose that the Nick/Address field in Nick Colors can accept multiple comma-separated addresses.
In the first example (taken place on Freenode), it would highlight based on user's either registered nicknames, or by his network services "cloak", or by his ISP address mask. The reason for highlighting based JUST on nickname is mIRC doesn't populate the IAL by default upon joining a channel, so the color will still take effect this way. The other two addresses in case he changes nicknames to something random or fails to authenticate with NickServ.
In the second example, two address masks for two different bots that are owned by the same person.
This method of comma separated addresses, supported by other Address Book features, will help keep the Nick Colors list tidy.