Yellow yolk
These yolks come from unhealthy chickens raised in factories that live in terrible conditions. They have no freedom, space, or natural sunlight and they eat grains only. They live in filth and a lot of them have been hatched from incubators, which is not a natural process.
Light orange yolk
These eggs usually come from local groceries and these chickens were also raised at big farms. Though they do not live in horrible conditions as the chicken in big factories, they still live in inadequate surroundings.
They lead a poor diet, comprised of grains only, without any natural foods which chicken enjoy and need in order to be healthy, for example, insects.