Someone once told me that he threw out raw ground beef because it was bad. Said person doesn't cook, so I wondered why exactly he threw it out. "Did it expire?" I don't remember what he said, but I think he didn't look. "Why did you throw it out?" It was grey.
To get to the bottom of this question, in case anyone wondered the same thing, I did a quick Google search, as well as conducting a personal test, to find out the answer.
The Google search said that when raw beef becomes exposed to air, the air reacts with the meat pigments, particularly oxymyoglobin and causes the outer surface of meat to turn red while the inner meat, not exposed to oxygen, becomes grey-brown. Hm.
It turns out that the innards of this meat was red. What I actually was searching for was a page telling me that red dye was inserted into meat, but I found some stuff about meat being packaged with CO or some such thing to keep the meat looking red, which does absolutely nothing for the freshness, and the meat is packaged in a way to either keep air out and the air it was packed with in, or to let a small amount of air in.
Back to the meat used in this post, both were purchased at the same time, and both were placed in the same section of the refrigerator, though one slightly froze while the other was completely "fresh". One of the pages I read said that if the meat was thoroughly grey, chances are it was bad, though you should also go by smell as well because I've used ground beef in the past when a) it was past the expiration date, and b) it was grey through-and-through, neither of which I'm suggesting anyone do and blaming me for your bout of e coli, I'm just letting you know I'm still alive and running.
To sum this post up, be one with your food. Part of cooking includes getting "in there" and closely observing what's up with your ingredients. If you go by sight, you'll end up throwing out grey raw ground beef that may be perfectly fine to cook with, and no one wants to be wasteful. Right?
The ground beef was turned into taco meat, though that's beside the point of the post. =P