We had some software that stored IP addresses in a field in a ':'-separated text line; luckily, the files were quite transient, so we could just change the separator into a semicolon and be done with it.

Elsewhere, the IP addresses were used as part of a file name on Windows; we replaced all colons in the IPv6 address with '!' to fix that.

There's bound to be lots of old software with similar problems around.