Pity there's effort going into colour schemes when nothing seems to be happening about the disgusting spam.
Well, phpBB comes with multiple themes as standard and it's a trivial task to add more. Removing the right of unregistered users to post would probably turn people away from a forum of this nature (and might be seen as hypocritical), and adding a CAPTCHA
means getting your hands dirty with source code, amongst other potential problems (see the link for more details). There's not really an easy way to get rid of spam short of deleting it as it happens, unfortunately.
..incidentally, it seems that there's no "Disable HTML" tickbox now, so the quote problem seems to be solved. Yay.