Not all EXTBANs on Freenode will contain a ':' colon, only those that carry parameter data with it. And though extban flags can't be stacked in Freenode, a forwarding '$#channel' can amend any ban, and colon can be used in those channel names as well as IPv6 hosts.

Code:
MODE +b $a          ... ban all registered users.
MODE +b $~a         ... ban all nonregistered users.
MODE +b $a$#c:olon  ... send registered users to channel #c:olon
MODE +b $z          ... ban all SSL users.
MODE +b $~z         ... ban all non-SSL users.
MODE +b $~z$#bu:tt  ... send non-SSL users to channel #bu:tt

Well. At least I won lunch.
Good philosophy, see good in bad, I like!