Juliette de Bairacli Levy reckons it's the chlorophyll in green plants that gives yolks their richness of color. She's a great author to look up for natural treatments.
Regarding ex-batt hens, I found that if you take an animal from a deprived environment and bung it onto the healthiest diet you can afford, their bodies go into a recoup mode wherein they either stop laying or lay inferior eggs for up to a year as they rebuild completely from the inside out. Then they amp up production again and you get eggs that match the best of your naturally raised hens, and they look worlds different from the pallid-pink crested, rough feathered birds they were.
Alternatively you can keep them on common pellets and keep up the consistent production combined with the sub-par health and lose them at the usual age to the usual problems. Cheaper, but no good if you wanted to include them in your own diet for your own health so you can avoid dying at the usual age from the usual problems, lol. Got too many health issues to remain on mainstream diets, my family does. Hit a brick wall, it's all organic and natural from here on. Expensive, but being normal got us to this point. Now it's costly to survive.