How old are your hens?
A hens age influences their egg colour and laying. See this is how things happen.
A pullet chick is born, now she starts to grow up. She has when she is born 2 ovaries,her left ovary has little dots on the inside. (if that is correct?) those little microscopical "dots" are future eggs. Now the Pullet is 19-25 weeks old depending on the breed, she lays her first egg. It might be a flop at first but starts to come right after a few tries. Her first year is her most productive year of her life, and she has well coloured egg-shells. Now she becomes a hen on her 2nd birthday. And production is still steady or is declining. Her egg shells are lighter and she starts to age.