The color of an egg is related to its ingredients. The yellow color of the egg white and yolk, with less ingredients and a shorter period of time, is called a variegated egg. If the yolk turns black, it's because the ingredients are heavier or it's been left for a longer period of time. If the yolk turns black, the ingredients are heavier or have been left in place for a longer period of time. Black eggs are called fluffy eggs, and pine or cypress branches have been added to the ingredients. In addition, there is to tell you, the skin eggs contain more lead, it is not advisable to eat more, often eat.