A BRIGHT red comb may mean your hen has a fever and is flushed. Blueness to the comb can indicate poor circulation or simply cold, the way your fingernails might get a bluish cast to them if you get very cold. Frostbite itself is usually indicated by areas of white (dead) skin that eventually turn black and fall off.
Keep in mind that the color of a hen's comb may change based on whether she is sleepy, she has just laid, she is excited or mad and so on, just the way your own complexion might flush or go pale in connection with your emotions, level of exertion and so on.
If you think your hen is ill, your best bet would be to consult with a veterinarian to get a good diagnosis and treatment options. Obviously, if her comb remains strongly blue or purple (or very pale) it may indicate a medical condition that needs attention. However, just like humans, some chickens may display their feelings or state with more obvious flushing or blanching than others, when there is no medical problem at all.