Male chickens are known as roosters or cocks or cockerels, females are known as hens or pullets. Castrated males are known as capons, but castrating chickens seems a silly and expensive option to some people who reckon its easier not to have a cockerel if they dont want chicks.
Cockerels are generally distinguished by larger head furnishings (combs and whattles) and colourful plumage (feathers).
Head furnishings direct the blood to the surface to keep the chickens cool. In winter, when its cold, chickens head furnishings may seem a little more pale than usual, this is because vasoconstriction occurs, which is where the blood vessels near the skin narrow and more blood is directed deeper down to conserve heat.