I once used a hyperlink styling technique that involved using linear gradients and text-shadow as an alternative to border-bottom. The benefit of this was creating underlines that would be broken by hanging characters, such as "g" and "j".

I soon realised that the underlines on the :visited state of my hyperlinks were not changing colour.

It turns out that :visited links ignore the background-image property. This is due to security, particularly because one could be able to track a user's movements and history based on the background image of a visited link.

Setting the background-color property will work but because gradients are not colours (remember, background-image is used to set gradients`), they are hit by this slight restriction.