Dave Arnold addressed a related topic on a recent Cooking Issues podcast. He was addressing steak cooked sous-vide, in vacuum bags (like me, D.A. almost always uses ziplocs; this only applies to vacuum-sealed meat).
Meat cooked in a vacuum bag, especially if it's purchased in cryovac packaging and cooked in that same bag, of if it's transferred directly from the store-bought cryovac to your own vacuum bags, tends to appear more rare than it is. He points out a number of ways in which color is an imperfect indicator of doneness, because factors besides temperature affect the color. He suggests letting the meat breath ... ideally, pre-sear it, and let it sit out for a while before vacuum bagging it. You'll lose a shade or two of blood-red with a medium-rare steak.
It's about the reactions of oxygen with myoglobin. When meat is its normal raw-red, you're looking at oxymyoglobin. When it turns the ruby-purple-tinged, Tarantino crime-scene red of vacuum-packed meat, that's deoxymyoglobin. And when you're looking at the grey-brown of overcooked (or overoxidized) meat, that's metmyoglobin.
We can probably come up with other ways to exploit this phenomenon.
