Egg yolk colour is closely related to chicken feed. If green leaves or corns are added into the feed, their colouring matter transfers to the egg yolk, reddening the egg yolk. Adding carotenoid into the feed makes the colour of an egg yolk look bright. This does not cause any adverse effects to human health, but increases the nutritional value of the egg. Consumers should buy inspected eggs from licensed premises and should avoid buying eggs of unknown sources or those which are unreasonably cheap.