I've had eggs that were fresh before, and they had a bright orange yolk, and I've heard from many sources that the orange color is a good thing. Our first egg was the same yellow as the store bought eggs. Does this mean that something is missing from their diet? They free range all day.
I give mine garden leftovers and flax. I notice if I forget to buy the flax they get lighter in the yolk dept. Some people use marigolds also to make the yolks brighter. You didnt mention the type of feed you use? The flax also give them better feathering (IMO) Its healthy for them. If you hens just started laying, keep in mind that first eggs are usually off in many departments. I have also read that corn improves the color. I give mine scratch. Access to plenty of plant material is also a plus.
Do your chickens free range and if not are you supplementing their diet with healthy greens? The hen that is laying a paler egg--could need more nutrients--but it could be a short term problem. Try giving them a bag of spinach or chemical free grass and see if the color improves...good luck