“Should I be concerned about a black eye after a mild head injury?”

I had a fall and hit my forehead on some concrete floor about 5 days ago. Went to the hospital afterward and they didn't find any signs of a concussion. They did a CT scan as a precaution and found nothing wrong there either. At the time, the impact area (right eyebrow) was merely swollen. Over the following three or four days though, an ugly black eye formed, possibly the worst black eye I've ever seen. My eyelid is dark purple, almost black, and there's bruising even below my eye. In the last two days or so, I've noticed a little bit of dull pain start to arise, including a mild headache. I've also noticed that vision in my right eye is ever so slightly blurred from time to time. Today the black eye has taken on a very green/yellow tinge, which I believe is a good sign.

The CT scan showed nothing wrong but I'm wondering if any of the symptoms I've described warrant a second look? Is there any risk of infection or gangrene or something? Is it possible that the doctors missed something in the scan results? If it were not for the fact that I'd had the CT scan already, I would think I might have a skull fracture or something, but that's supposedly been ruled out. Am I just being paranoid?

Thanks for any advice.