After a long time a new irssi upstream release hit the archive. While the most notable change in 0.8.16 was DNSSEC DANE support which is enabled (for linux, src:dnsval has issues to get compiled on kFreeBSD), the most visible change in 0.8.17 was addition of support for both 256 colors and truecolor. While the former can be used directly, for the later you have to explicitly switch the setting colors_ansi_24bit to on. A terminal support it is needed for that though. To test the 256 color support, your terminal has to support it, your TERM environment variable has to be properly set, and you can test it with the newly added /cubes alias. If you have an existing configuration, look at the Testing new Irssi wiki page which helps you get that alias amongst giving other useful tipps, too.
The package currently only lives in unstable, but once it did flow over to testing I will update it in wheezy-backports, too.