Now, in an ideal world all major HTML elements in all LiveJournal styles would have a CSS class or ID associated with it, so you can simply manipulate them to your heart's content in a stylesheet placed in the GLOBAL_HEAD override. Unfortunately, Punquin wasn't designed with this concept in mind, so I had to think of another way to do what I wanted to do.
And then it hit me: maybe I could insert arbitrary code into the colour values of my journal. If instead of white I put white" class="something, it would be stuck in a set of inverted commas as normal and would give me two perfectly formatted attributes as a result.
My initial tests went well, but the way LJ parses the colour value is somewhat erratic. I don't know how it's done - maybe somebody with an understanding of the code could enlighten me? - but in some cases it played merry hell with the HTML.
Punquin decided to be even more weird by behaving differently on the New Entries page from all other pages, and its Friends page is designed so as not to let you override FRIENDS_TALK_LINKS or FRIENDS_TALK_READLINK. So much for that. I managed to work around the different treatment of pages by overriding a couple of style attributes in the CALENDAR_HEAD, FRIENDS_HEAD and DAY_HEAD overrides.
Everything now looks great on any recent browser which handles CSS semi-decently. If your browser doesn't support Cascading Style Sheets, this journal will mostly look like crap. Sorry.