Thank you for getting back to me. There are many factors that can influence the quality of the yolks. The warm temperature can in two ways. Hens often don't eat as much when the weather is hot. They especially don';t spend as much time foraging, and the foraged foods lead to more color in the yolks. Many hens stop laying completely when temperatures are extremely hot. Eggs that aren't gathered very quickly in hot weather will lose quality in a hurry. Left in the nests for even an hour, yolk quality can quickly deteriorate. The yolk membrane will lose strength, making the yolk prone to breaking.
Certain antibiotics can lead to colorless, weak-membraned yolks. That's why I asked the brand of chick starter you use. Many contain antibiotics and if your laying hens have access to them, that could be the problem. even if they don't have access, it would be best to get your young pullets off of it soon. Starter doesn't contain the right combination of nutrients they need for egg laying.
Diet is the main cause of color in egg yolks. Feeding brightly colored foods usually leads to more colorful yolks, while pale foods lead to light yellow, or even nearly white yolks. Here is a website where you can read more about egg quality:
There are two more considerations. Some chicken keepers who had this problem reported that it disappeared when they changed laying mash brands. So, you might want to give that a try. There are certain weeds, that when consumed, can lead to diminished yolk quality. There is more on that on the site I gave you above.
There are some diseases that can cause weak yolks with little color. One called egg drop syndrome is a possibility, but often the eggs also have weak shells with this. There are usually no other symptoms except egg quality declines. You would have to consult a vet for diagnosis and treatment options.
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