The colon problem comes from the fact that the packages ks_meta variable uses colon as a separator:
http://git.beaker-project.org/cgit/beaker/tree/Server/bkr/server/model.py#n4946
But as far as I can tell Anaconda doesn't actually allow arbitrary RPM requirements in %packages, it has to be actual package names. So this isn't going to work properly anyway.
The real solution would be a harness which installs task requirements instead of putting them into kickstart %packages...
On Gerrit: http://gerrit.beaker-project.org/2991
This patch fixes the kickstart generation so that task requirements are passed through as is, even when they contain colons.
Note that this does not change the fact that Anaconda does not accept arbitrary requires in %packages, only package names, so things like perl(Archive::Tar) will still not work, although they will now appear in the kickstart correctly.