My hens yolks get a little paler in the winter time, because they are not getting as much green food. Usually in the summer they get some grass clippings, tons of extras from the garden and whatever bugs they can catch. I’ll occasionally throw them hay in the winter and they get any leftover food that we don’t finish, but that’s pretty much all the extras they get this time of year. They are still much brighter than store bought though.
The only color difference between the younger and older hens is the color of the egg shells themselves. They get lighter colored the older they get.