When some of our hens started laying eggs with paler yolks (we sell our eggs and those dark eggs are what brings in the money) we started adding kelp meal to the chickens diet. We had sprinkled kelp meal (powder) over their lay pellets and the yolks are much much darker orange now instead of that pale yellow we were seeing. All our birds free range part of the day and eat plenty of greens but the kelp meal seems to have made a huge difference.