While some people are put-off by the idea of "blood" in their cooked food, many commercial meat packers treat raw steaks with carbon monoxide to keep the red color because many grocery shoppers associate the color red in raw beef with freshness. It is also worth noting that the more myoglobin a meat contains, the darker/redder it will be. This is why some animals have red meat while others have white meat. Animals with red meat use more of their muscles for extensive activity and, therefore, have more myoglobin. Other animals like chickens have both white and dark meat, wherein the dark meat is found primarily in their legs and wings (because they are used for more physical activity.) Most fish are considered white meat. After all, floating and moving around in the water doesn't exactly require much muscle use. Others like tuna, however, swim briskly for longer periods of time and have darker meat as a result.
Who knew there was so much to learn about meat? We salute you, knowledgeable butchers of the world. Oh, and just to reiterate, never order your steak well done.