Short Answer: it's green or a dark brown or it smells
Long Answer: Actual fresh meat should be brown, but manufacturers put dies into it to make it look redder and more appealing to the public. If you have ever eaten deer or moose meat the meat is a brown color and not the bright red. It's true if you see a metallic green or the meat smell "sour" then "When in doubt throw it out!" Having food poisoning is not a pleasant thing to go through.
If you have frozen raw meat and cook it and there are left overs then you can refreeze it. YOU CAN NOT thaw raw meat and then let it sit around and refreeze it.
Believe it or not I smell all my meat as odd as it may seem especially ground round (for hamburgers) steaks and roasts. For chicken, chicken pieces or turkey I put in cold water with a 1/2 cup of salt and that kills any bacteria and then rinse well, pat dry with paper toweling and then cook.
"Color of Beef Beef muscle meat not exposed to oxygen (in vacuum packaging, for example) is a burgundy or purplish color. After exposure to the air for 15 minutes or so, the myoglobin receives oxygen and the meat turns bright, cherry red.
After beef has been refrigerated about 5 days, it may turn brown due to chemical changes in the myoglobin. Beef that has turned brown during extended storage may be spoiled, have an off-odor, and be tacky to the touch."