Many layers pellets have 'yolk inhancers' in them, even organic ones.
Technically is not chlorophyll, which is green but xanthophll and carotene, yellow and orange pigments which add yolk colour. 'greens' are full of these, you just don't see it behind the green chl. Carrots, pumpkins, marigold petals will really give a zingy colour.
Do they just get mixed corn, or pellets as well? Could be an inbalance of protein/carbs/vitamins which pellets might help.