This is a domdanda & response written by class 3 as of the Galileo Galilei Scientific High School of Spadafora (Messina) for Evidence Network Academy.
The yellow-orange color of the egg yolk is the result of a combination of factors, mainly related to the hen diet. The yolk contains carotenoids, natural pigments present in many plant foods, such as corn, grass, green leafy vegetables and flowers. These pigments, in particular lutein and zeaxanthin, are responsible for the yellow-orange shade that characterizes the yolk. The hens that consume a diet rich in these foods, such as the yellow corn, tend to produce eggs with darker yolks, while those fed with a poor diet of carotenoids produce clearer yolks.
From the clearest to the darker. Even if the color of the yolk can vary, this does not affect the nutritional value of the egg. However, a darker yolk can be perceived as richer in nutrients or tastier, but it is a subjective perception since the main color differences between the yolks are linked exclusively to the variety of nutrition and not to the quality or freshness of the egg.