|: The color change occurs in Safari
But it will be lost once you delete your browsing history. That's what causes Biff problems.
A better solution would be to store this information on the server. A prerequisite would be authentication. But I'm not sure if I want to use storage space for this. Although, lets see: The forum has about 8000 messages, so we would need about 8 MBytes to store this information for 100 users. Sometimes I get E-Mails that are bigger. But they don't need to be stored permanently on the server.