Egg yolks are really light- whats wrong

[Tready]

My leghorn is 5/6 months old and has always been a good layer, but her egg yolks are almost white. This picture has 4 egg whites from my Leghorn and 4 from my easter Egger, you can certainly tell the difference. Is this disease?

 

[Tready]

They spend all day outside foraging and only go to the coop for bed. The Leghorn eats more dried Grubs that’s the other chickens. (They’re her favorites and my kids are all too happy to oblige.) they don’t appear to be ill, they’re laying normally. We have had a bad infestation of flies that I have gone to war with using diatomaceous earth and water bag traps.