I am trying to write a php script to differentiate a real human visitor from a bot.

One idea I read about and what to use is having PHP print a page containing a invisible hyperlink to it's self.

This should make the links color purple or whatever a:visited color is set.

A bot does not render links, thus will not see color change. Therefore, if the links color changed we can be certain it is a real human and not a bot.

Is there a way to use javascript to get a link's color?