Meat in the stores is actually packaged with gasses such as nitrogen to make the meat redder, called MAP packaging (modified atmosphere packaging). It has to do with customer appeal which is why it is done. People will always choose meat that is bright red over meat that is slighly brown or dark red...even though the bright red meat is considerably older than the latter. Fresh meat is also dark red and not the bright red you see in the stores. As I said, they make it brighter red because of customer appeal. Meat is also treated with preservatives to slow oxidation. So, meat that is brown is not necessarily bad. Check the date and if it is old, then I probably wouldn't eat it. But, you leaving it in contact with oxygen has allowed oxidation to occur and turn the meat brown. It's probably fine.
EPIC.
