Looks like this (as in, display of ANSI escape-sequences in login banners) was disabled in OpenSSH as of v5.1p1: http://www.mail-archive.com/secureshell@securityfocus.com/ms...

Edit: I should add that it does work fine if you place the generated output into /etc/motd instead. The article argues that might not be the best place for it, I'll leave that for you to decide however.