OK, I think I figured what the problem is now. It's the session ID's in the URL's.
As soon as a page updates the link is no longer visited since it's a new session in the URL.
Are you sure???
When I made my last post, I considered that too so I also tested by first navigating away from the home page before trying a link, going back and then refreshing. That way I could be sure there was already a session id attached to the link and refreshing the page didn't alter it in any way.
If you tried my last code, there must be a conflict or override somewhere either in the <body> tag or some other inherited css class.
I always keep a 2nd installation and database running 4images on my site just so I can test things against the default installation setup. All I had to do was remove the "link", "alink", and "vlink" from the <body> tag in header.html and the code I previously posted worked flawlessly. Visited links remained in purple for the duration of my session.