A well-done steak should show no hint of pink whatsoever. Its center will be grayish-brown throughout and the outside will be nicely charred. (approximately 165 degree core temperature)

A medium-well piece of meat will just have a slight hint of pink in the middle. Otherwise, it will be primarily cooked through and will feel quite firm. (approximately 155 degree core temperature)

A medium piece of meat will have a large band of pink through the middle, but will be primarily grayish-brown throughout. (approximately 145 degree core temperature)

The center of a medium-rare piece of meat will be slightly warmer and reddish-pink instead of red. (approximately 130 degree core temperature)

A rare piece of meat will have a bright red center, and its outside will be brownish-gray. The center will be warm, but not hot. (approximately 125 degree core temperature)

Seared on the outside, completely red throughout. Meat remain gel-like in texture and difficult to chew; juices are not yet flowing freely. (approximately 115 degree core temperature)