I'd say they need more nutrition possibly. Some people feed colored foods high in beta carotene to help make the yolks more orange.
But nutrition rolls over to the yolk - the more nutrition, the more color. Were they ever wormed? You might consider worming them (since you're probably not going to eat these eggs anyway) with Wazine (piperazine 17%) twice - once, and then again in 14 days. Or once with fenbendazole (Safe-Guard paste horse wormer). With the fenbendazole, you give one pea-sized piece of paste in the beak for each bird. Repeat in 10 days.
Then do that twice a year at least.
Worms steal the nutrition from birds. Because they were in bad shape before, it takes a while to build that nutrition back up. Especially if the birds are laying.
Also, if you give them a treat of yogurt once a week, they'll absorb their food better and be slightly more disease resistant. The calcium and vitamin D in the yogurt help with egg shells. The live bacteria in the plain yogurt help with all food utilization as the bacteria are the workers that literally break down and make available what the gizzard grinds.
When you worm, you can feed those eggs back to them for the next two weeks or so. Boil them and them mash them up - feed that mixed with yogurt and a little sprinkle of crumbles in the morning. They'll be getting rich nutrition from the eggs and yogurt as well as protein to rebuild their feathers. It's ok to feed them their own eggs back after the worming or medicating.
By the way, the hens should be on a diet that consists of 95% good quality and strongly fresh smelling laying pellets (any protein percentage is fine). The other 5% of the diet can be treats like the eggs, yogurt, greens (don't feed a lot of spinach or kale), whole oats (great for condition and nice protein level). Be sure to provide them a separate container of granite grit (available in great little small bags at most feedstores) and mix that with oyster shell (also available in a similar small bag). Both serve different purposes - oyster shell being too soft to be grit, grit not providing calcium like oyster shell does. Hens can self-supplement a little calcium with the oyster shell. The yogurt helps provide vitamin D3 to make that calcium be absorbed.
Scratch, should you choose to use it, should only be given out in handfuls for them to "scratch" out of the bedding and keep them interested in the yard. It will otherwise dilute their nutrition and cause problems - like colorless yolks, bad egg shells eventually, bad feathering, etc. Thought you might want to know.
