Apply a distinct visited links colour in theme CSS

It's really handy, especially on large / complex / frequently used sites, to know where you've been. When winding my way through d.o, I am constantly frustrated because I visit the same pages again and again with little way of knowing beforehand.

Visited link colours solve this problem. It would greatly improve my experience if you set them using the a:visited CSS pseudo-element selector. I suspect it would help other d.o users too.