Have you wormed them? Worms or external parasites like mites will make the combs lighter in color too. For the first round of worming, try some Wazine-17. You put it in their water first thing in the morning when you let them out of the coop. Two weeks later, you should do it again. You will have to not eat the eggs for about 2 weeks after the wormings. I worm twice a year, once in the early spring, and in the fall. The second round of worming, I use a product called Eprinex. It will kill internal and external parasites. You apply it one drop at a time under each wing, on the skin, and also on the back of the neck on the skin. Check the threads on here for worming and other veterinary needs. You can buy both of these products locally from livestock centers, like Orschlen's or such. The Eprinex is marketed for cattle, and is a pour-on type of wormer. Do a search on BYC for more info.