How can I keep corned beef pink? I have a large gathering on St Patrick's day and serve corned beef. In years past I did all the cooking on that day and missed my own party due to all the work. Last year I cooked the beef the night before, let it cool overnight, and sliced it cold. I added water from the pot and reheated it in the oven in aluminum trays, and kept it warm in sterno racks. The taste was great but the color changed from pink to gray.

Any suggestions on how to serve a large group a hot meal and still keep the color of the beef pink would be appreciated. FYI, my typical method is to cook the beef first the night before, then in the same pot with the same water cook the potatoes, carrots, and cabbage on the day of the party.
As Jay mentioned, potassium nitrate or sodium nitrite is what gives commercially made corned beef its long-lasting pink color.  Home cooks can use the same chemicals.  Just make sure that whichever you buy is specifically labeled for use in food.  Also, since you mentioned that the corned beef you buy comes with a spice mixture, check the ingredient list to make sure it doesn't already contain either chemical.

I've only ever used potassium nitrate (A.K.A. saltpeter) for corned beef.  1-2 teaspoons per gallon of water is plenty.