The red means that something loaded in the page is not secure. You'll see that the security icon at the bottón right of the window is also broken.
This is common when you visit a page but only the data connetion is over https but the images are showed through normal http.
EDIT:
Replying to your last question... it doesn't means it's unsecure (the red one) but awares you about it. Maybe is unsafe but if you trust the site... I don't know, all is in your hand.
Edited 1 time(s). Last edit at 12/20/2007 07:49PM by JohnHell.