Use Inverted Colors to Highlight Active Link
http://www.smackthemouse.com/inverted

Tverskov, Jesper
Smack the Mouse
2006

Abstract:

It is often difficult to find the cursor when a web site is navigated using the keyboard. Where is the active link? With CSS the author of a web page can adjust how the active link is visualized. Inverted colors are the best way to highlight the active link.