littlebabyjesus
one of Maxwell's demons
myoglobin
So if your steak doesn't have red juices, it's overcooked, basically.
Oxygenated myoglobin is red, but when its structure is changed by heat or by other molecules, it changes color. That's why redness in cooked meat signifies juiciness: As meat cooks, the heat causes the other meat proteins to coagulate and squeeze out their moisture.
Myoglobin stays unchanged and red as the meat juices flow, then turns from red to gray-brown as the release of moisture ends and the meat becomes dry.
So if your steak doesn't have red juices, it's overcooked, basically.