What influences egg yolk colour?

What makes the yolk yellow? 

Carotenoids play the most important role in providing egg yolk colour. This family of pigments can vary in colour from yellow to red, and are occur naturally in many different plants, fungi and algae. In these species they are essential for their growth and photosynthesis. In humans, they play an important role in our immune system. Its carotenoids that make carrots, tomatoes and pumpkins the colour we associate with them. 

When healthy hens forage plants and insects, even animals sometimes, they ingest carotenoids. The pigments are absorbed from their intestines into the blood stream. The bird can then either use the pigments as antioxidants or to make Vitamin A, or they will accumulate within the yolk. 

What can cause yolk's to become pale? 

When you see pale yolks, it could either be because the bird is eating less carotenoids, for example due to prolonged housing and restricted ranging, or illness. If a bird is unwell, they may need to use their carotenoids as antioxidants, or to make Vitamin A to help their immune system. 

Healthy Hens will have lovely, rich yellow yolks if they are free range and eating a varied diet.