Found This think it was dried Marigold petals that my mate was on about.
Cheers Arry
"The commercial guys when they want a darker yolk, they use marigold petals, the powder from it. You can also use dehydrated alfalfa if you don’t want to go that route because you’re getting the dry foliage that still has the pigments in it," says Jacob. "So, typically a diet high in dehydrated alfalfa will give you darker yolks."
You can also give your chickens treats that are high in xanthophyll, such as carrots, apricots, pumpkins, red cabbage, and the leaves of most green plants.