During the winter here when it is colder and wetter, everyone's feet get more pink. I do not know the answer to state with conviction, but I *think* it is because they are cold and the blood circulation does up to keep the exposed parts warm- and they appear pink/flushed because of the increased blood flow. Like my own nose/ears/fingers outside. Could be also due to irritation from the mud. If there is no swelling/limping/asymmetry probably nothing to worry about. I do remember one of my roosters was always pinker than the others- he was the one with white legs- probably was just more visible on him than the yellow and slate shanked birds.
jess