Why don't you share your solution with us? It may help the next person.
As I understand it, the page is being served by a server on a different computer, but you want the Yun to react to a specific page being loaded? Seems to me you would need some JavaScript on the page being served that makes a request to the Yun (probably a REST API?) to control the LED. Or, the page could include a specific item, like an image (even if it's a 1 pixel invisible image) that is requested from the Yun, so that loading the page would automatically make a request to the Yun. My last idea is to have a CGI script on the remote server that accesses an API on the Yun when the page is loaded.
So, what solution did you discover?