I was at the feed store the other day and noticed some oyster shells for chickens to eat. I asked the guy what that was about and he sad if you chickens ever have soft eggs giving them this will harden them up in no time. I don't know about color but, I would ask at your local feed store about the oyster shells or something like it. Good luck. I would also ask them about the coloring of your yolk and all they might be able to point you in the direction of something to help. I think what I was told chickens eat rocks and stuff and for some reason this helps to make the eggs hard. There gizzard needs some to work properly, if they have been stuck inside all this time they probably haven't been able to peck around to find what they need. I would definitely check on the oyster shells.
