Layer feed is usually 16% protein, flock raisers and grower feeds usually range in the 18 - 20% protein range. I feed 18% flock raiser year round. Most treats will dilute that, which is why treats are recommended to be no more than 10% of the diet. Some foods or ingredients can be harder to digest, or can change the color/consistency of droppings. It can affect all birds, a few, or only one. The one you mentioned that caught my eye was kale, greens can definitely cause changes. Eliminating it all for a period to see if it improves will help see if it's a contributing factor or not.
